Is this black beard algae? It has just started appearing on the tips of my plant leaves.

My C02 and lighting is on 7 hours a day in two sessions of 3 and 4 hours respectively. C02 starts and ends an hour before lighting. I does thrive plus every other day, and change 50% water a week. Tank is 75g with substantial water flow. Feeding once a day, and I'm pretty sure my fish think that's not enough..

Would some H2O2 do the trick here? Tank has 75 amano shrimps in it that don't touch the stuff..

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That’s BBA. In my personal experience, it shows up when the CO2 levels are inconsistent. Flow does help with distributing the CO2, but I ran into this when I was using a small canister system that constantly ran out leading to gaps in CO2. I also had an older regulator after the canisters that was inconsistent in working pressure that resulted in me having BBA.

It’s hard to get it to disappear. After I got my CO2 levels to stabilize and be consistent, to get rid of the old stuff I ended up having to spot treat with H2O2. It’s tough to eliminate but it’s easy, IMO, to stop the spread.

Thanks for the advice. My CO2 canister is 3 liters and as far as I can tell the solenoid is working fine. I will give the affected areas a H2O2 bath and hopefully the problem goes away.

I have a large airstone in my tank, and I divide the 24 hour day into two light and two dark periods, with CO2 shutting down an hour before 'sundown'. Could this coupled with the high surface agitation from my filter power head cause CO2 to dissipate too quickly during night periods, leading to a CO2 instability?

Looks like BBA. H2O2 is good at killing it, but won't stop it from coming back.

It looks like you're using ADA soil, is that right? How long have you been using it?

And how much Thrive+ are you adding each time?

Using Tropica soil. Tank has been going 10 weeks now. Using 5 squirts of Thrive on Tuesdays, Thursdays and Saturdays. Thinking back now I recently exchanged my lily pipes for a power head, so the BBA outbreak may be associated with the increased flow.

Very much a possibility.

I can induce BBA on command by increasing flow too much. Especially turbulent focused flow.

That's interesting about the increased flow = increased BBA in some setups. I'm not a believer of strong flow and think powerheads are an unnecessary eyesore in most setups. I wonder if the increased flow deposits more organics in certain areas. More than the system can deal with. These deposits might be able to settle into the pores of slow growing plants, rocks, even plastic.

You know I am not sure. Fablau also said could be more detritrus stirred up and in the water column.

But I can tell you this. Not too long ago I put some new motors on my filters. Holy smokes the flow was MUCH higher. Within days I had BBA on my driftwood, which I hadn't seen in a LONG time.

CO2 extremely stable. Ferts all the same. No other changes.

Reduced flow and it went away.

I see a lot of people mention fluctuating CO2 levels as a cause. What they should be saying is poor CO2 levels. Poor CO2, dirty tank, too much light are usual causes. But it's been pretty well documented that it also seems to love areas of high flow.

And I agree with you, good flow is poorly understood. Too much (or wrong kind) has no value and can create problems.

Quick update for those interested. I spot treated the visible bba with h202, then halved my flow rate. No other changes. A week later and no visible growth. Since my tank is pretty clean, I'd say this lends support to the bba likes flow hypothesis.