Tiger Barbs in Distress

[Otter2009]

I did some tank maintenance yesterday where I did about a 40% water change and cleaned a fair bit of green and brown algae (as well as a bit of blue-green algae) out of my tank. As per usual, all of my tiger barbs hid while I was doing so. There was one exception that was swimming in a more open part of the tank with its mouth apparently stuck open. I completed my maintenance with no other weird occurrences.

Later that night, I found my some of my barbs gasping for air at the surface and discovered that the solenoid on my CO2 regulator hadn't shut off properly. I turned off the CO2, re-positioned the filter output to give the tank a fair bit of surface agitation, and left it over night.

Today, the CO2 levels are next to 0 but my barbs all seem off. Some are just lethargic but others are exhibiting more concerning behaviors such as swimming head down, and being uninterested in food. There's also one that is missing. I can't find a body so I'm not sure if it's dead or just hiding.

Does anyone have any ideas what may have happened? I had a similar occurrence a few months ago after tank maintenance (without the CO2 issue) and can't seem to figure out what's triggering my barb's distress.

Parameters:

36 Gallon

Ammonia - 0
Nitrite - 0
Nitrate - 10ish
pH - 6.8 (This is higher than usual. It's usually about 6.4)

[libertybelle]

Maybe just having difficulty recovering from the ph swing? Keep testing to make sure there is nothing wrong with the water but you may just need to wait it out to see if they recover.

Usually distress after a water change or filter maintenance means either overcleaning triggered a mini cycle (unlikely in this case since you don’t see amm/nitrite) or another parameter swung too much for them to be comfortable. Ph/ temp of new water being the most common.

If the ph of your tap is much different than the ph of your tank you may want to age water / slow down water changes or do smaller changes so it doesn’t stress them out

[Otter2009]

Good call on the pH. I guess that after I turned off the CO2, it spiked. Today, it read about 7.4. Unfortunately, I've lost three of my barbs up to this point with another one that is not doing so well.

I haven't turned my CO2 back on yet which leads to the question: Would it make more sense for me to try to turn it back on and get the pH back down to where it should be or to keep it leave it off and hopefully stabilize the pH?

The other thing is that for a second time, one of my barbs is swimming with its mouth wide open. Any ideas what that is about?

[Autumnsky]

Can you make sure the oxygen and level is up.

Add a air pump maybe, to get the oxygen flowing.

It is possible the fish was ill affected. Or got a rock or food stuck in his throat.

[libertybelle]

And re: the co2, swinging back down would probably be counterproductive. I’d vote for stability right now and then once things have settled you can gradually restore your co2 use.

[Otter2009]

Unfortunately things have not gotten much better. My CO2 is now back on its regular schedule but I'm still losing fish. The trend of them swimming with their mouth open before dying has continued as I'm still not sure what to make of it.

I've also had a massive algae bloom and my nitrates are now reading 0 (likely being consumed by the algae).

Thoughts?

[Autumnsky]

What kind of algae, and can you start reducing your lighting some each week?

Are you dosing phosphorus? Feeding too much?

[Otter2009]

It's mostly green hair algae but there is some brown algae in there as well and a small patch of blue-green (which has been there on and off for the past month or so). I'm currently not dosing any fertilizers although I have used Thrive in the past. I also only feed a small amount once per day.

Throughout the tank's life, I've tried several different lighting schedules and have always run into algae issues.

[libertybelle]

Gasping can be ammonia; have you rechecked ammonia. Maybe your ph swing triggered a mini cycle?