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Re: [APD] Aeration & a planted tank

I had incidents of unexplained fiish deaths that occured only at night then 
discovered fish gasping in the morning when my first tank was fairly new -- 
2 months old. Even the snails in the tank had clustered in a corner with the 
fish the morning I saw the problem. This was a CO2 injected tank with 
pearling levels of growth. CO2 not injected at night. Fish levels were low 
to moderate for the tank but in a two month old tank I can't say the load 
was low for the plant and bacterial biological filters. The tank was 
moderately to heavily planted at the time, and probably a bit closer to 
 I don't have an O2 testing setup, but I suspected ammonia was the culprit. 
Ammonia tests were negative, nitrite tests were negative. That left O2 
levels as the only culprit. The cannister filter return was a modular Eheim 
setup that ran perpendicular to the surface of the water. Water returned 
through small holes drilled in the return pipe with the first hole about 3 
inches under the surface. I changed the setup to make the return parallel to 
the water surface and turned the pipe so the holes are slightly angled up. 
Fish death and morning gasping stopped. 
 The amount of surface agitation created by this method is much less than 
what arises from an airstone with a Rena 50 air pump. CO2 consumption to 
maintain levels increased negligibly. The only significant change other than 
the end of fish deaths was that the crypt planted below the return pipe grew 
dramatically in the current. I think originally there was an inch or so of 
still water at the top of the tank. There is now reasonbly strong top to 
bottom circulation on the return end of the tank.
 I've never seen this problem in my non-CO2 tanks but I think the reason is 
that they all have surface agitation from filters and low fish loads.
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