Pond Boss Forums AERATION Should I aerate? diffused air vs. pumped water at surface

Some background info first....and an apology for this long post that follows......Last November I renovated my 1 acre pond in the Sierra foothills (~1600 feet elev) east of Sacramento CA (a great story for another time). Pond is tear drop shape ranging from about 8 to 15 feet deep with mostly steep sides, almost no shallow areas. Pond will receive no supplemental water from May-November (thanks to our Mediterranean climate) but will hold good volume until rainy season returns. Based on past experience, it will likely lose 2 to 4 feet to evaporation. I anticipate aquatic scum/oxygen depletion as the greatest threat to fish (not yet stocked) and overall water quality. I know I need to aerate. And the question is........on a limited budget (I can't spend more than $2k for a system and am expecting a 20 to 30$ per month increase on electric bill) what system has the greatest bang for the buck (1) a surface aerator that pumps water from several feet down and sprays it out to break up, chop and ripple the water surface to inhibit algae and provide modest oxygen replenishment, or (2) a bottom up air diffused system that will destratify pond, provide a lot of oxygen, but not break up surface water very much (low-modest algae control).

Was reading some material from "Ken's Hatchery and Fish Farms" in GA that suggests bottom up air diffusers can be dangerous to fish because they circulate, and do not release to the surface air, the ammonia and other organic breakdown gases generated at the pond bottom. My gut says bottom up air diffusers would work great......would like some input before I continue to spend money on this great hobby......

Thanks,
Dave in El Dorado, CA

Nice size pond! I only a 1/3 acre. Since there is no in-flow, that presents it own host of problems including holding toxins, and temp issues. I am rasising rainbow trout with depth avg of 8 ft., but pockets of 2-24 ft. under about 1/3 of the pond.

I aerate ALL winter and the results have been great, though this coming winter I will move the diffusers out of the deep areas toward the 6-8 ft. areas.

Having no shallows is a real plus for you as deeper and colder waters are the key conditions to limiting algae blooms.

With up to 15 ft. (a nice depth) and stepp sides (no shallows, that is good. But your real downfall is no in-flow. I have over 20,000 gallons a day flowing in from an artesian well (15-17 gpm) and am adding a second well this week to give me more cold water and more overall replacement during summer temps etc.

You do need to aerate and de-stratify tyhe water or else your great 1 acre size and nice depths become unusable for the fish. Imagine if you live in a 2000 sq. ft. home but there is no oxygen in the basement and as summer comes, you can hardly breathe on the first floor? where would you live??? Of course on the the second floor. Same idea in a heavily stratified pond, especially with no rain during half the year. If you do get alot of wind, that would help, but not "trunover the bottom very well.

I use a 1/4 hp 2 diffuser system from Stoney Creek distributors. jsut looked up their web-site and it is not working. I think it was the Gast 1/4 hp unit with the two rubber membrane diffusers. I would much rather have the vertex diffusers- that look to be mroe effective. This 2 diffuser system was actually made for ponds for up to 1 acre.

To keep elec costs down and maintenance minimal, make sure to get the 220v model what ever you get. 220v motors are far more efficient than 110- 120v motors.

I currently installed a timer on the aerator and just run it at night. I am going to install a Johnson Controls A419 (about $65 incl. ship) temperature controller next week, which allows me to set the control to turn on when the air temp drops to a certain temp (like 57) regardless of day or night. Raising trout I can't afford to convection heat the pond. Running the aerator into June about 3 years ago killed all my trout- nicely aerated, but way overheated the depths (live and learn. When the temp drops to 57 I get a nice aeration effect and a cooling effect at depths, while de-stratifying the "anoxic" layer. And I don't have to monitor when the temp drops.
If you have elc available, I would go with a 3 diffuser system and up to a 1/3 hp 220v motor and add teh A419 temp controller (mostly used in greenhouse applications).

horrible typing above- sorry! Ok I'll use the preview fucntion more! It should say - 12-14 ft. pocket of deep water, NOT 2-24. . .

ME

Thanks for the quick reply. I should probably add that one of my goals is a happy bass/bluegill population (temperature should be less of an issue than with trout).

Lucky you on the artesion well (what State are you in?). Yes it would be nice to have supplemental water, but thats not currently an option (some day when I'm rich I'll drill another well on property to supplement pond water).

I like the idea of a timer. I've looked at Vertex systems and liked the one with two diffuser stations (8 total diffuser plates), but it seems a bit pricey. Seems like a good company (responsive salespeople), with a good product, maybe they'll negotiate some on price. There are a lot of sales pitches out there, so I wanted to talk to Pond Boss readers and posters to find out what is really working in the field. Many cheaper systems using air-stones are available, but for similar electrical demands (20-30/mo), would these be effective for my volume of pond?

When we renovated pond, I built several craters on the pond floor (at different depths) rimmed with rocks for fish structure. I was hoping that whatever system I choose can get oxygenated water circulated into the structures so they dont end up being anoxic fish traps.

Dave I sent you a PM, Ted

Dave:

Do you get enough rain in the Winter to flush water from the pond after refilling?

Dave in el dor, Some of my thoughts;

1. Bottom diffuser system is best & most economial to buy and run for your needs.

2. Runing the compressor on 220V will only save money if you are using 3 phase electricity, otherwise basically same cost as running at 110V.

3. Running at night during heat of summer may help reduce evaporation from surface bubbling activity.

4. Ken's Fish Hatchery and others are wrong about aerators releasing ammonia from pondwater by aerating. It does not happen. Some dissolved gasses are released during aeration but ammonia is not one of them. Ken's catalog is in the process of revision to imporve the information.

Good Post Bill,

Ammonia is not lifted and "de-gased" by aeration. It is taken care of indirectly by nitro sonoma and nitro bacter bacteria. (I learned that with my first aquarium when I was 10).

Dave, the surface of a lake can absorb over 0.2grams of oxygen per square meter per hour. Photosynthesis will add additonal oxygen too. These two points illustrate that almost any eutrophic lake can be 'aerated' by mearely 'circulating', wich uses much less energy than a floating surface aerator. By choosing a firm that not only manufactures quality equipment but also has the formulas, the practical experience, and the equipment to do the work with a cost within your budget, you will have a system that you will be happy with for many years to come.

A turnover rate of at least 0.75 times per day will satisfy the oxygen demand of most ponds and lakes. There are cases where heavier nutrient loading will reqiure higher rates. Roughly calculating, your pond contains 2,427,641 gallons. If for example you install one diffuser system in your pond, you will be turning over that volume about 2.2 times per day.

A simple 1/3 hp wobl piston compressor will cost you $24 per month at $0.07/KW Hour running 24 hours per day. You can run it at night only and as Bill mentioned, reduce the evaporation potential and reduce your electrical cost.

My concern is that the rotary vane compressors, (a good compressor) my be harmed by the start and stopping and pushing 7psi each time it has to start up. The compressor is like a plane lifting off, it is at full force until it reaches altitude (depth for the compressor) and then it backs off and levels out. The wobl piston compressor will be able to push up to 30 psi without any damage. The rotary is rated for continuous use at 10 psi and max at 15.

...My thoughts

First I want to thank all who provided input.

Theo, we get a lot of rain in winter. My guess is that the entire volume is replaced many times during one wet season. My little rain guages measured 55.3 inches this season (its usually 30 to 40). The season is about over now. The pond basin lies within a seasonal creek drainage and there is no way to control input to the pond because of the (steep) topography. So the entire watershed drains into and out of our pond. As you might expect, we get a big influx of sediment and nutrients, but it seems to clear out in a couple days after the highest flows. I created a sediment trap on the upper end of the pond by building a ~70 foot long, ~6-8 foot high rock damn. The rock we excavated right from the pond bottom. The water rushes in from the feeder creeks enters the sediment basin, and drops most of its load in the slow water before gently rolling over top of rock dam which was surveyed and graded in about a foot below high water. After water enters main basin, slow flow continues over to a large concrete and bridge timber spillway (designed ~30 years ago by a very clever rancher). The upper catch basin will need cleaning out every few years especially after the flows we had this year. Long answer to your question, but wanted to give you a good picture of the pond dynamics.

Of coarse, after creeks dry up, and there is no more spillway action, the water just sits, evaporates, grows algae and waits out the summer.

I guess one question going back to the diffused air vs. surface circulators (or fountain types) is.......is a good diffused air system as effective as a surface system at inhibiting the floating mats of filamentous algae and other scum? From some of the posts it seems one assumes it will work as well if not better. As of today, our rains stopped about a week ago, temperatures have climbed well into 80's, algal growth is going nuts along pond edges, floating mats just starting to form. So far this spring, one pair each of geese and mallards had their kids, a wood duck visited, and the treefrogs, bullfrogs, 10 billion polywogs, and pond turtles love it so far. The food chain is there and ready for oxygen and bluegill stock.

Also, thanks (Bill, Cary, Michael, Ted) for the info on the types of pumps, very informative for somebody who knows only about rocks. Unfortunately, here in sunny CA, PG&E hits us up for 12c/kWhr up to a baseline level. Above that it goes to 17c/kWhr, and above the next level it goes to 22c/kWhr. Our normal monthly house usage puts us near (sometimes above) the first baseline. So adding the aeration system will likely keep us in the 17 to 22c/kWhr.......Too bad Arnie (our governator) cant help me with that.

I'm gonna have to pick a system within the next week and get er done. Cant dilly dally much more. Sounds like a piston type pump, couple diffuser stations, weighted tubing is the way to go. I have a 20 amp feed within 50 feet of the pond's edge (I believe its a 110 breaker, but not sure). Probably could be changed to 220 pretty easily by someone who knows what their doing (if needed).

Sorry for being a chatty fingerling, but I enjoy talkin to y'all, does get kinda lonely up here in the hills, just one guy against an acre of potential pond scum, I do greatly appreciate the feedback.

Neither aerator will do much to keep your filamentous algae suppressed because the primary nutrient source for your FA is the inflow water which is laden with dissolved nutrients. Those nutrients will grow some type of plant, that is what dissolved nutrients do. Surface disturbance from a fountain has minimal impact along the sides or edges in shallower water where FA thrives. I think the diffused air system will do a better job of reducing filamentous algae that grows due to the nutrients that are released / recycled from anoxic (oxygen starved) sediments which will be suppressed by a bottom aerator. But as I said your FA (at least early spring growths) are due primarily to dissolved nutrients from watershed water not from nutrient recycling from thermal stratificaion. No form of aeration suppresses nutrients entering a pond from runoff.

Don't bother switching the power to 220V unless your electrician says 220 on single phase runs cheaper the 110. An electrical engineer will also be able to verify this.

I don't think you should go out of your way to get a rocking piston compressor. Although it will work adequately in your situation, but if you can get a good deal on a rotary vane compressor based aerator system take it. I have had many GAST 1/4hp rotary vane compressor units running so far for 6-8 years with twice daily on/off cycles with no problems so far. If you have a good check valve system at the diffuser and you keep moisture away from the pump there is minimal effort on the compressor each time the system starts up. Moisture can cause problems with compressor start switches.

Thanks Bill. Is your preference for a rotary vane based on the increased volume of air they can pump? I am just now learning about pumps, pump systems etc.

In general, between piston and rotary vane pumps, which require more maintenance? I've seen info indicating rotary vane types require more frequent rebuilds. Your units that have gone 6-8 years have not required rebuilds in that time? That sounds pretty good.

The air volume produced between a 1/4-1/3hp rotary and a 1/3 hp rocking piston is similar. The benefit of more air volume increases with the rocking piston as the depth gets deeper than 18ft-20ft. Rocking piston compressors are the best way to go when depths are deeper than 18ft. Rotary vane depth pumping limits are 18-20 ft.

Cary and I are not talking about standard piston compressors. We are talking about rocking piston compressors which are different than a standard piston air compressor. Rocking piston compressors have a rubber cup type diaphragm/piston/s versus a piston compressor that has a metal piston with compression rings similar to a car.

Rebuild intervals for rotary vane pumps are based on primarily two features. Pumping depth (max operating presure) and running time. The vanes have an hour-life running time on them (10,000hrs) and this can be extened by decreasing the depth that the pump has to push air to. The higher the air pressure the harder the vanes grind against the metal rotor cavity. A shallower depth of the diffuser (max pond depth) and less pressure to relese air results in longer vane life. A lot of my clients in the north, only have to run their aerators 3 to 8 hrs per day, thus 10,000 to 14,000 hours for vanes takes 6 to 8 years or more. Some guys with smaller shallower ponds have gone 10 yrs and still running on their first set of vanes. It all depends on run time and maximum pressure during operation. 24/7 compressor run times at 18 ft deep and vanes may last only about 13-16 months. Replacing vanes is a very simple job and takes about 15-20 minutes; 30 minutes max. Replacing the rubber cups on a rocking piston compressor is I think quite a bit more difficult than replacing vanes.

Thanks Bill.

The max depth would be 14-18 feet depending on exact deployment position of diffuser station. I also want to run a second station in 8-10 feet of water further up the pond. However, the pump location is another 20-30 feet above pond level. I have a ~50 foot dry run down a steep bank to reach pond's edge. Does that additional elevation change (outside water) affect pumping conditions? Tried to attach a pic, not sure how to do so......(tried copy/paste, and drag/drop neither took).

Dave, Additional elevation should not affect the pumping. However note that each diffuser will need a valve (ball valve) on a separate air line to regulate the air flow. Otherwise all the air will want to go only to the shallowest diffuser. I prefer to split the air at the pump with a manifold and valves. However some get it done by splitting the air at the water's edge. This exposes the valves to the elements and often causes extra problems.