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#511690 09/17/19 03:27 PM
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I am struggling with the concept of DO levels in my little 1/4 acre pond.

The aeration system currently runs from 3am to 8am and the water temps and DO readings (among all the other test results) are consistent throughout the water column when the system shuts off, so I know the pond is getting successfully turned over at least once and probably twice by my calculations in this time period.

Last weekend's morning tests resulted in water temps at 75 degrees F top to bottom, DO levels at 4ppm from the surface down to about 2-3 feet, and secchi reading at 23". Aeration had just shut off for the day and by the time 6pm, rolled around, I had the following test results...

Water Temps - Bottom 75 F - Top 82.

DO - 6.5 ppm @ surface, 4.9 ppm - 12" down. 4.0 ppm - 24" down.

secchi - 23" (stayed there all day long)

This suggests to me that the current algae bloom is really helping the upper water column with respect to DO (still not all that great really). Whereas the aeration system appears to not do so much for me. Maybe it is keeping the DO from really falling off at night, but it kinda looks like it's ruining the upper levels of water.

I am wondering if mixing in the algae bloom at night is hindering the overall DO levels. My thought is that an algae bloom strengthens during the day, makes decent O2, then at night it gets mixed throughout the water column and has to struggle again the next day to build back up.

I am currently going to gradually increase my air time and check the water next weekend to see what it does.

Somebody straighten me out...surely I'm missing something in my logic. AND, what should I try to do to improve these DO levels?


Fish on!,
Noel
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I don't aerate, I rely exclusively on algae blooms. However, we have completely different bodies of water. Considering you secchi disk readings, I would be inclined to favor more aeration. The clearer your water becomes, the less you will have to rely on aeration. Mud bugs will ensure you always have turbid water to a degree, necessitating aeration.

Also, the bottom of your pond is the key to the water quality. How thick is the muck on the bottom?

To state it simply, I don't have a clue smile

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Originally Posted By: Joey Quarry
To state it simply, I don't have a clue smile


Nice Joey, that was good for a laugh!

I don't think the muck can be all that thick as the pond was renovated in late 2017, but I don't go to the bottom much. The sediments are probably a few inches thick as the aerator bases seem to be hard to pull up off the bottom, but sediments and muck, in my book, are two different things.


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Noel
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You may want to sample the bottom of your pond to see what is happening down there. Is it sediment or muck and how deep? If it is muck, as your water becomes more clear, i.e. crawdad boil, you may want to put a diffuser on the bottom to create more aerobic conditions.

Since it was recently renovated, you'll have a good idea of your pond management practices the past 2 years by sampling the bottom.

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QA, I am hoping some others chime in but your late afternoon surface readings seem (IMHO) to be indicating lower than they probably actually are. These readings of surface water should be near saturation IHMO (saturation would be about 8.4). Are you confident in the instrument's calibration?

With regard to muck, I don't think you have much ... if any ... though the mud may well be very soft and hydrated on bottom. My son found a crayfish on fishing trip about 3 weeks ago and took it home for his aquarium. Quite remarkable the clean up it has done in such a short amount of time even recycling fish waste. I would have never guessed they could make use of that kind of food but it has grown noticeably and has already molted. We have supplemented his diet with a very small chunk of hotdog every 2 or 3 days ... so he has had some meat too. I mention the crayfish shredding activity only to highlight that they effectively recycle detritus and thatmuck will be slow to accumulate because of them.

Thinning the crawdads appears to be making a big difference on your water clarity.

Last edited by jpsdad; 09/20/19 06:13 PM.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers


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Originally Posted By: Joey Quarry
You may want to sample the bottom of your pond to see what is happening down there. Is it sediment or muck and how deep? If it is muck, as your water becomes more clear, i.e. crawdad boil, you may want to put a diffuser on the bottom to create more aerobic conditions.


I'll contemplate how to get the sample, but I'm not sure what to look for other than the depth of the muck and how it smells. And, I am confident that my diffusers are circulating the water from top to bottom and getting what DO I have down there .


Fish on!,
Noel
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Originally Posted By: jpsdad
QA, I am hoping some others chime in but your late afternoon surface readings seem (IMHO) to be indicating lower than they probably actually are. These readings of surface water should be near saturation IHMO (saturation would be about 8.4). Are you confident in the instrument's calibration?.........

Thinning the crawdads appears to be making a big difference on your water clarity.


I have cross checked the DO Meter with my Chemtech vial test kit, on occasion, and my confidence level is high.

I will remove more craws next year, if necessary, to further improve clarity but for now I am happy with some improvement. The water tends to clear up in the winter months anyhow.

EDIT: for clarification, when I say surface DO I am talking about the top 6" as the meter that I use has a 5" head on it that must be moving in the water to get a good reading. I bob it up and down as close to the surface as I can which means it's reading somewhere in the upper 6 inches.

Oddly enough I have measured DO levels as high as 11ppm at the surface, but just 24" down it was 4.8ppm.

Last edited by Quarter Acre; 09/18/19 09:14 AM. Reason: added 'Edit"

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Noel
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So, I have brought the aeration system up over the last week and is now running from 10pm to 9am and plan to bump it up another hour or two tonight for water checks tomorrow. They are calling for rain, maybe, today and tonight which the pond could use due to surface pollen floaties, but I'd just as soon it held off until after the water checks to keep another variable out of the mix.

I will check the DO tonight just because my curiosity with respect to the effects of the added aeration versus evening DO is eating at me.

Any more suggestions for my weekend's testing efforts?


Fish on!,
Noel
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Disclosure: I don't know squat about aeration.

Would there be a benefit to turn off aeration totally for a period to establish a baseline of how the pond is "naturally?" Possibly the same for any other inputs like feeding etc?

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Crayfish can cause turbidity issues in fisheries which lack dense enough populations of apex predator fish to manage their populations. Are you experiencing turbidity issues? I have significant unwanted experience navigating this issue - let me know I will help in any manner possible.


Many men go fishing all of their lives without knowing that it is not fish they are after. ~ Henry David Thoreau

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Originally Posted By: roundy
Disclosure: I don't know squat about aeration.

Would there be a benefit to turn off aeration totally for a period to establish a baseline of how the pond is "naturally?" Possibly the same for any other inputs like feeding etc?


That would be an interesting thing to try, but for the time being, I will trust that aeration is a good thing for my pond. The pond is suffering from heavy pollen and I am in the middle of a Optimal feed trial, so I don't want to turn either off right now. It will be cooling off more very soon which would normally call for more airtime, so I think I will test what more air does first and then turn off and test the DO trends later this fall. And, I will certainly run plenty of tests next spring before the diffusers are engaged.


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Noel
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Originally Posted By: teehjaeh57
Crayfish can cause turbidity issues in fisheries which lack dense enough populations of apex predator fish to manage their populations. Are you experiencing turbidity issues?...


My summer secchi readings where 11-13" all summer UNTIL I recently removed 150 crawdads: 4-5" long. Within a week the muddy looking waters cleared to 22-23" and has stayed there...so, I would say that the craws are mostly to blame. I plan to enter next season with a close eye on clarity and remove some more craws. I have done some throw netting and have only caught larger craws. I suspect my original stocked craws have grown out in front of my game-fish and need to be eaten down. Next year's clarity should be improved one way or another (trapped and/or foraged).

Originally Posted By: teehjaeh57
...let me know I will help in any manner possible.


I am open to any and all suggestions...thank you!


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Noel
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Good, manual trapping helps reduce populations - well done. What are your fishery species again? General population dynamics of apex predators? Have you experienced general reduction in macrophytes/FA due to dense crayfish populations? My .25 ac pond had all vegetation and algae denuded due to crays - my BG and RES couldn't keep up with YOY and had far too many adults. Even a few SMB couldn't help the situation, had to drain, seine, and start over [4 times!].


Many men go fishing all of their lives without knowing that it is not fish they are after. ~ Henry David Thoreau

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QA are you concerned that low DO has killed some of your HSB?


It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers


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Originally Posted By: teehjaeh57
...What are your fishery species again? General population dynamics of apex predators?...


I stocked 42 HSB, 500 HBG, & 90 RES. These went in the pond spring of 2018 after a full year of FHM explosions. Dynamics??? Not sure I understand the question, but here goes...The two HSB I caught earlier the this year were ~2 pounds and ~16" long. My catch records show that every time I have caught one, they have gained in size or were similar. I've not caught a runt HSB. The HBG tend to be in the 0.4 to 0.6 pound range. I have some recruitment, but the largest ones are less than 4 inches and most are in the 2 to 3" range with wavering populations of 1/2 inchers. I think the HSB are doing their job along with low recruitment. The craws are probably a predator of the YOY/eggs also. The RES have not been seen since stocking, but snail populations are low now. I have not seen any dead fish except a few, maybe 10, within a few days of stocking...mostly RES and two HSB...leaving 40 in the pond. I put in about 300 craws during the first two years. 90% of them were between 1 and 3" long. The remainder being up to 4".

Originally Posted By: teehjaeh57
...Have you experienced general reduction in macrophytes/FA due to dense crayfish populations?


The first two years had minor FA mats (5-10% surface coverage during the wort off the summer) that were mostly removed by me and water clarity trended during those summers around 18-24". The winters provided water clarity that got to 36". This last winter, I ran a shallow diffuser in one corner and the water stayed muddy with 12" clarity that remained throughout the summer until recently when the 150 craws were removed. Best I can tell, no other factors contributed to the turbidity improvement. FA was only in the upper few inches of the water this summer. Growing on grasses that leaned over into the pond, Water Hyacinth roots, and the dock edges. No floating mats were ever witnessed. FA has been absent for a month or better. I can only conclude that the turbidity reduced FA development, the craws kept the shoreline shallows cleaned up, and my freshly renovated pond is low in muck and nutrients.

Originally Posted By: teehjaeh57
...My .25 ac pond had all vegetation and algae denuded due to crays - my BG and RES couldn't keep up with YOY and had far too many adults. Even a few SMB couldn't help the situation, had to drain, seine, and start over [4 times!].


I have Pickerel Weed, Arrowhead, Thalia Dealbata, Botswana Wonder, & Mud Plantain, growing in the absolute shallows which do not seem to be succumbing to crawdad feasts. The Arrowhead seems to become craw food once it dies back in the fall, but during the growing season, they leave it alone.

I'm not sure what you mean by..."my BG and RES couldn't keep up with YOY and had far too many adults.". Does this mean you had way too much recruitment?

Anyhow, Starting over 4 times is TRUE dedication...the goal must have been very important to you.

Originally Posted By: jpsdad
QA are you concerned that low DO has killed some of your HSB?


I do not believe I have lost any fish to low DO or anything for that matter. My assumption is that I still have all my stockers and I see minimal recruitment. Lately, when I feed, the HSB and HBG will eat for as long as I throw feed. The last two weeks I have been feeding for an hour a night and throw in 0.25 to 0.35 pounds of Optimal BG (and some Optimal trial feed which, so far, has been 4mm round pellets). My fish do not frenzy during feeding...they take their time and stay spread out. I have been wondering that lower DO levels may be the cause. Feeding in the morning is practically a "no show". The DO levels during this time tend to be between 4 and 5 throughout the water column (aeration mixes it all in), but at night (aeration off all day), the DO levels are more like 6 to 10 in the upper few feet.

All in all, I am very happy with my pond, but worry about increasing biomass and seemingly low DO levels. I have not culled any fish for the dinner table and would prefer not to until the HBG are in the one pound range.


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Noel
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I am trying to determine if my pond is better with aeration running at max levels (summer temp driven) or if leaving the water to stratify, stay clear in the upper water column and maintain a consistent algae bloom is better.

Basic questions that keep running through my mind is...Is it better to have good DO levels in the upper few feet OR weak DO levels throughout the water column? What more, if anything, can be done to help DO levels in my BOW?

This morning's DO checks proved that the upper 3 feet of water was at 4.3ppm throughout the range (Temp and PH was also very consistent from top to bottom). I have to assume that the entire water column is at that 4.3 level due to the air running all night. This evening, I expect to see higher DO levels at the upper few feet.

I was hoping that I would see better DO reading this morning as I have bumped the air run-time from 5 hours to 12 hours over the course of the week, but the 4.3 reading is where the AM readings have been (roughly) for the last 2-1/2 months. The one time it was considerably better (5.6ppm) was during 24/7 air run times following a surface scum outbreak.


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Noel
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QA,

I feel wholly inadequate on the aeration questions but I would like to give you something to think about that may help with DO.

In addition to thinning the crayfish as needed, consider adding some additional shredder type forage. Hyalella Azteca and PK shrimp. Beyond the forage, I think they would help to keep your water clearer. They will be more abundant if you continue thinning crayfish and they may actually inhibit some of the crayfish foraging activity in the sediment in that they are also crayfish prey. Having clearer water will help your DO and these shredders will help to reduce the amount of decaying matter returning the nutrients to solution. Deeper sunlight penetration will boost photosynthesis and water clarity will help predators find prey and home in on your fishing lures. Both the fishing and DO should improve by reducing turbidity.

Last edited by jpsdad; 09/21/19 11:17 AM.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers


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Jps, I'll do some research on the Hyalella Azteca and PK shrimp and look forward to getting some. What I know about the PK shrimp tells me that they need some good hiding areas (the right habitat). I don't think my pond is conducive for them just yet...next to no shallows and what shallows are their are practically void of micro structure. Just the same, I will do more reading and work towards creating the right habitat.

Thanks for your advise, truly appreciated!


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Noel
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Here's some data from this weekend for contemplation. I invite all thoughts on the subject as I am very new to water DO/chemistry and could use all the help I can get. First off, nothing about my pond indicates that it's current DO conditions are bad. I think I can contribute the slow feeding habits of my fish to lower DO, but beside that, I don't see anything wrong. I have just read "somewhere" that my DO levels are of concern.

Aeration ran Friday night from 10pm to 9am.

DO levels Friday night at dusk were...

6.5 ppm at the surface,
5.2 ppm 1 foot down,
4.3 ppm 2 foot down,
4.1 ppm 3 foot down.

Sat Morning DO levels were 4.3 from the surface down to 3 feet.

Sat @ 1pm...

6.3 ppm at the surface,
5.5 ppm 1 foot down,
4.4 ppm 2 foot down,
4.4 ppm 3 foot down.

Sat @ 6pm

9.6 ppm at the surface,
6.5 ppm 1 foot down,
4.5 ppm 2 foot down,
3.8 ppm 3 foot down.

Saturday was overcast 95% of the day with a slight breeze at the pond.

pH ranged from 6.3 to 7.4 depending on time and depth.

Water temps were 76 to 79 depending on time and depth.

Ammonia, Nitrates, and phosphates were all Zero all day.

My question still stands...Is it better to have good DO levels in the upper few feet OR weak DO levels throughout the water column?


Fish on!,
Noel
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Just curious, how far off the bottom are your aerators? My guess is your aerators are a few feet off the bottom.

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3 foot off the bottom... One in 10 foot of water, the other two in 6-7 foot of water.


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Noel
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If you have your reasons, then disregard the free advice...

Aerators are generally poor at adding oxygen to water. Roughly, 1.5% of the oxygen diffused is dissolved in the water for every foot of depth. When it comes to diffusers, deeper is usually better.

Also, since your diffusers are 3 feet off the bottom, your bottom is stratified and anaerobic.

Unless you have your reasons, it may be worth experimenting with the diffusers at the bottom of the deepest part of your pond. Note of caution, depending upon how stratified your bottom has become, harmful gasses could be released when you first begin true bottom aeration.

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Experimenting with the depth of the diffusers may come into play next year if the water continues to clear. They started at 18 inches off the bottom and were moved up to 3' to help with clearing the water. That did not have the effect I was hoping for. Removing crawdads seemed to be the ticket, so the diffusers may go back deeper.

With that said, I do not get a thermocline or stratification with my setup even with the diffusers set to high. I believe, equal temperature readings from top to bottom prove that. After the aeration has run, the temps are within 1 degree which indicates thorough turning of the pond. After the aeration has been off for 10 hours, the only sizable temp difference is at the upper foot of water which can be 10 degrees during the heat of the summer.

Maybe if I could run the aeration 24/7 there would be improvements, but Midwest summers dictate nighttime runs in my small pond. This has me scratching my head regarding the DO readings that I get. With cooler weather approaching I hope to get the aeration system up to near 24/7 and look forward to the resulting DO checks.

My fear is...with the air system on full time, it thwarts the benefits from the O2 producing algae blooms by turning them to the depths of the pond where they can't get good sunlight. Of course, I have no scientific proof that there are algae blooms present other than the green color of the water where it used to be more brown from crawdad mud stirring.


Fish on!,
Noel
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what is a good D.O. meter probe that y'all would recommend?

thanks

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I am reviving this thread from last year as I am still concerned with the DO in my pond. I am still finding that the DO levels from 6" at the surface to 36" down after the aeration stops in the am to be low (3 to 4ppm). The evening readings are...

________Surface (@6")____24" down______36" down
DO______ 6.2____________3.5____________2.3
PH______ 8.1____________7.8____________7.7
Temp_____82 F___________71____________69

I have calibrated my DO meter with 7.0 PH buffer solution and it calibrates the DO level off of the outside air oxygen content...so it should be working correctly. Last year I cross checked the meter with a vial-type DO test kit and it matches. I believe my readings to be good, but I am going to do some research on the instrument and double check my methods of calibration.

My well water reads...DO = 3.9, and PH = 7.7. My fish might be better off in my well. LOL

The massive amounts of bullfrog tadpoles are visibly absent in the am, but swarm the surface gulping at the surface in the evening. I never see fish piping at the surface. I threw a 7-8' net yesterday for 40 minutes off the dock and removed over 400 tadpoles (into the creek - my wife asked if I counted...of course I did). I averaged 20 TP's per throw with a max catch of 40 in one throw. Right, wrong, or indifferent...I think that removing biomass will help. I will remove more TP's today along with trapping out more crawdads to help improve water clarity. I caught only a few 2" HBG young during the netting process BTW.

I only run the air at night to avoid heating the pond and have thought about running it 24/7 to help with DO, but 3-4ppm readings after it shuts off does not encourage me much.


Anyone out there have DO readings to compare with respect to air run times and such?


Anybody have any advise to offer?

Last edited by Quarter Acre; 06/02/20 11:11 AM.

Fish on!,
Noel
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