Help With Floating Algae

[Michael from Daytona]

Not many people are considering climate change as a contributing factor to unstable pond conditions. "It's the first time this has happened" is a common report from folks who have been stewarding fish for years. I live by the ocean in central Florida and am confronted for the first time in my four years of ponding by a green alga that stays submerged until sunlight hits the pond. At this point gas (presumably O2) from photosynthesis causes the algae to become buoyant, rise and converge on the surface (ponds 22" deep) in mucousy globs that can be skimmed best by moving the net very slowly. Otherwise the globs break up into tiny particles that pass through the mesh. My skimmer filter becomes clogged in just a few days, as does my pressurized mech/bio+UV filter. At dusk, the photosynthesis stops and the algae sink to the bottom.

I used Algae-Fix and Sludge Destroyer in their proper dosages, to no effect - although the latter seems to improve water clarity. I have had extensive potted water lily and Alisma plantago plantings as well as 60% surface coverage by water lettuce - but this year the koi attacked the water lettuce roots so I had to remove and isolate the lettuce in a separate tank to let it recover. I checked pH and was surprised to find it was between 8.5 and 8.6 - when all the literature was saying most pond imbalance problems were connected to low pH. Nitrogen and phosphorus levels have never been a problem.

Anyway, I added a cup of vinegar diluted in a 3 gallon pail to my two 600 gallon ponds and the pH dropped to 7.3 over an afternoon. My suspicion is that algae love a basic pH and that is why the Algae-Fix failed to produce results. I intend to reintroduce water lettuce and will provide netted root protection until the lettuce population is re-established.

I think another underlying problem was that a month ago I repaired a broken/leaking concrete shell that was cracked by a heaving tree trunk in a heavy windstorm - and did not seal the fresh concrete. In addition I used several unsealed concrete blocks as planter supports in the repaired pond, and the leaching effect must have pushed the pH up in both ponds. The fishes' behavior has not changed throughout this episode.

Finally, I think that several of my koi (10 in one pond, 10 comet goldfish in the other) have grown to the point where their pond suffers from fish overload. Given the two ponds are connected, if one becomes toxic, they're both toxic. I should probably cull the herd - but the most beautiful fish are the big ones and I just couldn't part with them.

We'll see if maintaining a less alkaline pH will aid in algae control.

 

[Jhn]

@Michael from Daytona, a lot of the first time this has happened has little to do with climate change in regards to our pond. more to do with your final thoughts, what your experiencing your fish have gotten bigger and your filter system/biofilter can’t keep up with the waste being produced, hence the explosion or sudden appearance of algae when it has never happened before. Eventually, you will need to rehome those koi if your ponds are only 600 gallons, as they are going to overwhelm the biofilter despite your best efforts.

Dumping chemicals in there like algae fix is a waste of money at best and can be counterproductive at worst killing the algae which then consumes oxygen, killing the fish.

 

[Lisak1]

Climate change? No. Ten koi in 600 gallons - or even 1200 connected gallons - is a recipe for disaster, which you already know. Algae should never be the primary problem that you try to address in a pond - it is only a symptom, and in fact can also be part of the solution. The real issue is an overabundance of nutrients, waste, organic material, etc in the pond feeding that algae. And the algae is doing it's part by keeping the pond from becoming toxic to your fish. Eventually you will lose that battle though.

And you may also wish to consider that dropping your pH that quickly can also be extremely hard on your fish. A pH of 8.5 is not a concern - stable pH should be the goal.

 

[brokensword]

ditto to all Lia and jhn said; lowering the pH over so few hours is very harmful. The fish need time to acclimate. Each point in pH terms is equal to 10 times increase/decrease.

You can protect your water lettuce by building/buying floating nets.

 

[Mmathis]

Wow, that’s an awfully drastic pH drop! Did your fish tolerate it?

 

[poconojoe]

Totally agree!
That's beyond too many koi.
They keep growing and maybe even multiplying.
Your pond hit the tipping point, it's not climate change.
Stop adding algaecide. Too many horror stories where all the fish died.

Rehome some fish or better yet, build a bigger pond!