Ok, here's the story:

The water in my 180G has been looking murky lately, which I attribute to my relatively high fish load. To compensate, I attached an air pump to the system to pump around 1 bubble per second which gets chopped up by my pump and fed into a canister filter.

Before I attached the air pump, pearling in my tank was very low. There was some pearling, but you really had to look hard to find it. 24 hours after attaching the air pump, the tank was pearling very heavily, and 2 of my discus were dead.

I have two questions:

#1: Could the combination of the pearling and the air pump create a high enough O2 concentration to kill the fish? I'm assuming the answer is yes because nothing else in the tank was changed. This is a stable tank that has been doing well for a long time. Another observation is that one of the remaining discus has O2 bubbles stuck to its fins - they look almost embedded. It looks like the fish itself is pearling.

#2: Why does adding air to a tank increase pearling from almost nothing to very high levels? I understand that if the water is more saturated with O2, the bubbles will stay on the leaves longer, and will be more noticable. But we're talking a major increase in pearling with heavy streams of bubbles rising from almost all of the plants.

The air bubbles are sticky, so that's what you may be seeing, you likely had poor CO2 to start with if there was little pearling.


It's possible the idea about CO2 mist can work using air alone, I've seen evidence for this in water fall areas and moss presence, they seem to grow mainly submersed below such locations(willow moss etc).

High O2 is pretty hard to do in our tanks to the point of lethal levels, 200% , 15ppm or more etc.


Regards,
Tom Barr

But is it possible? Taking into account that I have a strong pump which is chopping up the air bubbles very finely, and they then go into a canister filter which is pressurized at 12-14 PSI?

Are cheap O2 test kits generally accurate? I'd be curiuos to test, but not curiuos enough to buy a Lamotte kit.

Can't imagine what else could have suddenly killed seemingly healthy fish.

No, not with your system, the max O2 with the method you have is 7-8ppm max.
About 100%.

Aeration can never go beyond that, only if plant/algae growth is dramatic or if the water is both very cold and very deep (60inches or more).

Supersaturation can kill by gas formation in the eyes generally.


Regards,
Tom Barr