Pond Boss Forums AERATION Should I aerate? I murdered our fish

I humbly ask for advise. Just found this site and am overwhelmed by the expertise. 2 weeks ago I treated our pond with Avast(fluridone) to kill a 90% coverage of duckweed. Within a week there was a severe fish kill: catfish, bluegills and bass. The Avast supplier said the likely reason was a low level of dissolved oxygen caused by the extensive coverage of duckweed and warm water conditions. The pond is in no.Ky., 1.7 acres. 3.6 ft. av., 3- 4 stone Aquatic Eco aerators at 9, 7 & 5 ft., 3/4 hp rotary air pump. There is very high inflow of rain water. Much of water shed is cow pasture and a couple of septic systems. My questions are: Why didn't aerators protect the fish? Do you agree with supplier that membrane style aerators would be much better? Do you think the severe duckweed infestation is caused by dangerous pollution ie fecal coliform? I will appreciate any insights you can give me. Thanks very much.

Cliff, sorry to hear of your situation.Duckweed at 90 % coverage is a lot of plant material to decompose and takes a lot of DO. Your aeration system with a Gast rotary vane is probably a 1023 model which would supply 2.9 (approx) CFM per diffuser. 8.8 at 10 psi (your guage probably reads 7 PSI) Even though those diffusrs dont turn a lot of water at that depth I doubt that any brand of diffuser would of made a difference.I believe Avast (floridone)will be persistant for 30-90 label speaking.Your 1.7 acre pond with diffusers placed at 9-7-5 ft is not as efficient as you could be. You have enough pump to place a 4th diffuser and you may want to consider this only because of you lack of depth. The question is always what to do with your current airstones. You may want to do a DO check in the future and figure that with a water temp of for example 75F that a DO saturation level would be 8.4 ppm (at sea level)any where 70%-100% of this is great.(and obtainable) It also sounds like a nutrient test is in order to see what kind of battle or "war" you may be fighting. Read the diffuser information at www.aquaticaeration.com or click on my homepaage which will take you there also.Send me an email anytime with any questions you may have.PS I do know that Sonar (floridone) comes in different formulations that release in different stages and perhaps this may have helped. Kelley D or Bill C or some of the experts in that area may give you some feedback also.Keep in mind that the duckweed is your symptom and you have treated it, now look into what problem caused the symptom and go after that.As your symptoms will just return if you dont Ted

Aerators did not protect the fish because the oxygen consumption from the decaying plants was greater than the oxygen added by the aerators and DO levels dropped (probably very morning)below 2 or 3ppm. Chemical killed and or inhibited photosynthesis of all underwater aquatic plants so no oxygen was produced by them. Thus basically only oxygen source was bubbling action which was not enough in your case. Bottom bubblers are primarily water mixers not water oxygenators despite what most people believe. Bubbles from diffusers in shallow water are in contact with water only a very short time, oxygen is not very solulable into water, and air only contains about 20% oxygen. Some oxygen gets into the water but not a lot. Diffuser bubbling is not a real effficient way to oxygenate water. YOU PROVED that fact. Membrane diffusers for your situation in my opionion may not be a lot better than the AES stones. I would want to see good apple for apple tests/proof before agreeing to that info.

"Pollution" is cause of duckweed but it is not due to fecal coliform or e-coli. The bacteria are just associated with the "pollution" (animal manure/nutrients). Occurrence of duckweed is a sign of hypereutrophic conditions (very nutrient enriched w/ lots of organics). Hypereutrophic conditions will continually and always cause some sort of plant problem nuisance or infestation as long as the conditions persist. Your run-off water contains some of the very worst "stuff" as far as nutrients are concerned in managing a pond/lake. Some might consider it a glorified, aerobic, (mostly oxygenated) septic tank with occasional dilution from rain events. Hypereutrophic ponds have frequent fish kills if they are not properly aerated and still fish kills sometimes occur.

You should think of ways to stop the polluted runoff and get estimates to redig the pond. It is too shallow.

In dissecting the original comments, I'm drawn to a different theory.

Sometimes, I wished I could get fluridone to kill aquatic plants in one week - particularly during rainy periods when it is difficult to maintain plant-lethal concentrations for 30+ days.

However, in 15+ years of use, I have NEVER seen fluridone kill anything -much less duckweed- in less than 1 week, which is exactly what would need to happen for your treatment to cause a DO crash so quickly. So, assuming the indicated time-line was correct, I'd propose a different theory.

High nutrient loads, frequent inflows of nutrient-rich runoff - presumably interlaced with periods of cloud cover & temperature swings, etc. Isn't it possible that these variables may have prompted the DO crash?

I guess my questions for Cliff are: Had a large portion of the duckweed population (biomass) actually died and begun to decompose within one week after the fluridone treatment? Or, was your indicated time-line incorrect? Also, did you notice any significant shifts in your water color (green to clear)?

Though it is possible, I've never seen or heard of a fish kill caused by a plant biomass crash after a fluridone treatment.

Cliff, I'm not near as educated as Bill and Kelly but I have had problems with duckweed. The crap covered the other moss and kept light out which used more oxygen than created. If we had any clouds, oxygen dropped fast. I fed my fish every day and anytime they didn't come up as well, I knew it was time to manualy pull out duckweed. I'm draining and starting over this year.
Bill, I thought membranes were always better. I put mine together for maybe $35. Are you saying his pond isn't deep enough to be stratified?

Gentlemen, thanks to all very much for the quick responses.Ted, thanks for the email offer. You may be sorry you offered. Ted & Bill, I will try to arrange DO and nutrient tests. I think we are stuck with the cow pasture. Redigging the pond is apparently something we will have to do as the upper end is extremely silted and the muck is deep. Kelley, I agree that it seems that the kill was going to happen soon even without the fluridone. The timeline I gave you was correct. The kill happened within the week. I did not notice that the water had much color before the treatment but it was extremely clear after the kill.
How about some more bad news? I visited the club this morn. It's a great place. We have 99 acres,4 ponds, trap, rifle, pistol & archery ranges. The 1.7 acre pond in question dumps into a 9.5 acre pond. I have kept the 1.7 drawn down 6" to try to keep the duckweed contained. Also have a floating barrier of pipe insulators around the spillway. Our problem in the 9.5 lake is a growing coverage of watermeal. I cannot find watermeal mixed in the duckweed in th 1.7 pond and there is hardly any duckweed in the 9.5 pond, just a few plants. As you can tell I am not qualified to handle the magnitude of these problems. I have read that fluridone will kill the watermeal but I am not prepared to suggest that our club spend the large sum required. Do you know anyone in our area, near Cincinnati, that we can consult?

I really feel safe in saying that the fluridone treatment played NO ROLE in the fish kill. One week simply isn't enough time for it impact any plants (not even their photosynthetic capabilities).

I think some other variable(s) came into play, spiking the BOD and/or dropping the DO level below the tolerance of your fish.

Improper or overly agressive herbicide and algaecide treatments are often to blame for some DO-crash fish kills. However, in this case, the fluridone treatment should not be used as a scapegoat. Keep looking for the real cause.

Good chance the fluridone did not cause the fish kill. Maybe you are not a fish murderer!. At least not just yet. But maybe when all the duckweed does die another kill or DO crash will occur.

Kelly makes a good case of fluridone not causing the DO crash. Yes, if the duckweed was not all dead when the fish kill occurred then the fluridone-duckweed association did not cause the DO crash. Brian's experiences with duckweed blanketing the surface and inhibiting light penetration shed light on what likely helped with the lack of DO production below the surface.

My question is does fluridone kill phytoplankton? I am not real familiar with its method of action on each type of plant.

If it does kill phytoplankton, I would think it should not take a week to kill one celled plants. Loss of some or all of the phytoplankton community coupled with already low DO conditions from surface shading and shallow water makes for a soon to happen fish kill esp if you get a few cloudy/rainy days.

Also any septic or pasture runoff or additions will contain organic solids that upon further decomposing from bacteria action will consume additional oxygen from the water (BOD; biological oxygen demand).

Your DO crash was probably caused by several factors working together. Ponds and lakes are complex and they are acted on by numerous internal and exterior influences.

BH - Membranes have advantages and air stones have advantages; both have disadvantages. I'm not sure airstones produce larger bubbles than membranes. Bubble size is the main advangtage or benefit of a diffuser. In my opinion good quality airstones when positioned and ganged correctly produce the same water movement (gph) as membrane diffusers when each unit receives the same amount of air. NOTE, not all stones are built the same way, some are cheaply made and some do not produce uniformly small bubbles.

Main benefit to membranes as I see it is their ease of cleaning.

Let's see if Ted Lea (aeration guru)is reading this thread buried under the topic of "murdering fish".

What did I "say" that led you to think the pond was not deep enough to be stratified?

Fluridone is a carotenoid inhibitor in susceptible macrophyte plants, and has NO direct impact on any form of algae. Carotene production is halted shortly after the treatment is applied, BUT only on post-treatment new growth. Therefore, it takes several days or weeks for initial symptoms (chlorosis) to even appear, subsequently leading to photosynthetic failure and disruption of the impacted plant's capacity to sustain itself.

In less confusing terms: fluridone prevents susceptible plants from producing carotene, which is a substance that protects the plant's chlorophyl from harmful wavelengths of sunlight (somewhat like sunscreen lotion helps to protect humans from sunburns). The green chlorophyl in post-treated plant growth (now lacking the protection of carotene) is "bleached out" by sunlight, prompting the unusual and varied symptoms in affected plant-parts (reds, purples, whites, pinks). The affected plant eventually exhausts its nutrient reserves as it continually attempts to put on new growth - which doesn't survive and cannot photosynthesize "nutrient assets" for the healthy portion of the plant. In short, the plant's nutrient "account" is bankrupted. In the end, ironically, it is sunlight that literally kills the plant - fluridone is simply the catalyst.

This mode-of-action is the reason why fluridone is generally applied as the targeted plants' experience their most active growth period - usually in the spring (although duckweed growth-flushes occur in the early summer).

Footnote: I have one customer who asserts that the initials "A.S.", which follow the names of both fluridone brands (SONAR A.S. & AVAST! A.S.), stands for "ALGAE STIMULATOR" (though it really stands for "aqueous solution"). The customer's rationale for his assertion has some merit, since the release of nutrients from the decomposing plant biomass often spurs a tremendous filamentous or planktonic algae bloom.

Bill, I ASSUMED. Since I thought membranes moved more water and you said that maybe not better in his case, moving more water in an unsrtatified pond wasn't going to do much. Make sense?

BH - Membrane diffusers do not necessarily move more water. Amount of water movement (benthic aeration) is a function of air volume, water depth, diffuser size, and bubble size. The main difference, as I see it, between stone diffusers and flexable membrane diffusers is the ease of cleaning and degree or rate of clogging of the pores.

Kelly - I am an algal taxonomist not an algal physiologist and my botany background is sort of weak. I did a little review of algal physiology. As I thought all algae possess carotenes and at least 1 or 2 types of carotenoid acids. There are at least four types of carotenes alpha, beta, gamma, and epsilon. Beta carotene is present in all algae types or groups but at concentrations of 5%-20% compared to 30% of total pigment in higher plants. The algae gametes have higher concentrations of carotenes. Chara and Nitella contain "large" amounts of gamma carotene.

Knowing all this I am still confused why fluridone has little affect on algae. Is it because of the low concentration of carotenes they are less affected?

Bill - you pose a good question for thought regarding fluridone's selective activity on (some) plants, yet not on algal forms.

As I recall, fluridone blocks a specific biochemical process through which certain plants (but not all plants) produce carotene (which types of carotene, I do not know).

Also, fluridone-susceptible plants respond to varying concentrations of fluridone; with Eurasian watermilfoil normally being the most sensitive (usually somewhere around 3-10 ppb), followed closely by hydrilla, then coontail, Najas and several Potamogeton spp, etc. - each with a progressively higher threshold of tolerances. Sometimes, even different biotypes within a given specie may have significantly different responses to fluridone. Many emergent plant species have a relatively high tolerance to fluridone, or are completely resistant to its chemistry (ex. Sagittaria, Scirpus, Juncus, Vallisnaria). Among the floating plants, duckweed, watermeal and Salvinia are about the only susceptible species. Waterhyacinth and waterlettuce appear to be virtually immune to fluridone.

My statement that fluridone has "NO impact" on any algal forms may or may not be completely accurate. There are A LOT of different algal forms. It is also possible that disrupting carotene production in algal species would require a cost-prohibitive concentration of fluridone - yet "could" be impacted to some degree or another. However, Chara, Nitella and the various filamentous algal species do not exhibit ANY impact from typical fluridone treatments - and often appear to actually thrive after a fluridone treatment due to the release of nutrients from the decomposing macrophytes. Therefore, I would conclude that fluridone (typical dosage) doesn't block the process through which these organisms produce their specific types of carotene.

Interesting tangent: When Eli Lilly first discovered fluridone (late 70's?), they were initially excited about its prospect as a cotton herbicide - since it could be applied and incorporated in a cotton field and nothing - except cotton - could grow there. Obviously, cotton's unique physiology is completely immune to this herbicide compound. However, in the absence of sunlight (photodegradation), fluridone has a severe "carry-over" problem ~ meaning that treated fields could not be rotated into different crops (corn, milo, etc.) for at least two seasons. As every cotton farmer knows, growing cotton behind cotton (two consecutive seasons) is an invitation for cotton root-rot (a fungus) to set it and render the land useless for cotton production. Therefore, fluridone was abandoned for use in cotton production.

BC: my chemical book states that "fluridone has little effect on algae". Interpret that statement as you may.

Also, in aquatic environments, fluridone is degraded principally by photolytic processes - with an avg half-life of 21 days in pond water and 90 days in hydrosoil.

Plant-tolerance to this compound is directly associated with the plant's propensity (or lack thereof) to translocate the active ingredient to the site of new shoot growth. Unless the compound becomes concentrated at a growth point, its effects are greatly restricted.

Kelly - Interesting and good information. Selective herbicides are a very positive step in pond/lake management. We need more types of herbicides like that.

Murdered fish to aeration guru all under the same thread. "YIKES" Bill C yes I found your post. This topic of airstones vs membrane diffusers has been covered by myself here on PB and at my site at www.aquaticaeration.com but let me touch on some of the highpoints so not to make it sound like its not worth rehashing because it is and we have many new members and some that perhaps have not done the searches yet. One can not toss the term of "rubber membrane diffusers" into the same bucket as they are varied and numerous as aeration equipment salesman. The vast majority of rubber membrane diffusers are designed and sold to the wastewater industry who use them in a completly different fashion to a large degree to accomplish a multitude of different goals.See the Ecologix diffuser web page for specifics in the wastewater industry. I mention these folks as I see a few Ecologix 350 14 inch diffusers from time to time.Most of this type of rubber membrane diffusers produce a 1-3 mm bubble and require a range of 2.3 to 5 cfm. That would take a GAST 0523 (a great little rotary vane pump)which produces in the range of 3.6 CFM at 10 psi to power up 1 diffuser and you still would have no idea what your water turnover rate is at any stated depth.Why not take that same pump or a similar Brookwood rocking piston pump and utilize 2 and in some cases 3 Vertex Airstations and circulate from 5500GPM to 8300GPM instead and have the diffusers placed throughout the pond instead of at one central location. If you push Ecologix for this turnover rate at given depth and CFM's information like I have you may conclude at some point that they do not have it as pond and lake aeration is a tiny little sideline market for this diffuser company.If one would like to for example turn the entire water volume over twice per day as works very well in old nutrient rich ponds here in Ohio then one must have an idea what the water volume is in the tank (approx 325,000 per acre ft) and then know what the pump and diffuser unit are capable of producing.This brings us to the commercial part> The independent test data of a Vertex Co Active Airstation is published record with comparisons to AES Airstones and Otterbine (again see my site and diffuser section)Other rubber membranes are not in these tests because they are wastewater diffusers.The majority of the bubbles from the Vertex unit are .5-1 mm thus give it the low CFM requirement and the largest tested turnover rates in the aeration industry.These are not waste water diffusers. A 12 ft diffuser placement depth that produces turnover rates of 2778 GPM at 1cfm are simply unheard of with airstones and other rubber membrane diffusers.A 4 stone AES ALA 4GL is in the range of 1250 GPM at 1.5 -2 CFM Warranty is also an area that often comes up, Vertex offers a 5 year no question no hassle warranty on their diffusers, and you never remove them from the water to clean them, simply flex the membrane to clean them.So are all rubber membranes created equal ? as always ask the tough questions and do your homework before you buy.