Fish gone lethargic after installed chiller

mushy coral · Apr 27, 2026

I have just installed a chiller for my 20G tank yesterday. After i finished the tubing and stuff, i turned it on and let it run to bring my tank from 28.8c down to 26.6 in around 30mins. At that time, fishes and invert still fine. Then i went out for 3-4 hours and came back. Lights still on but my 2 fishes in their sleeping spot and seems to be sleeping. I did not think much and let them be but this noon i found my hogfish lying on the sandbed and trying not to turn up side down. There were 2 possibilities that i thought of. First: the chiller cuts off most of the flow and since my tank doesnot have skimmer, the oxygen in the tank now in danger level. Second: contamination from the chiller. I bought it new and i did not flush it, just straight away use it so the water could run though the chiller core and carry some of the contamination back into the tank. I did put in 2 airstone, went out to buy a skimmer and did a 30% wc, also added carbon. Till now, the hogfish is not seem to be better, the forktail blenny did swim out in the open and chase some floating particle for a moment but now it back to sleeping. The inverts include: a bta, a bleached donut, a japanese toadstool, 2 small jawbreaker mushroom and 4 turbo snails. The toadstool is shedding so im not to worry when its not open. Donut and mushroom completely fine, so as the snails. The nem started to move around and this noon it detach from the rockwork and float to the sandbed, i kill the flow, put it back on the rock and left it there so it can attach again. It got its foot cling onto the rock now. So the issue now back to the fishes cause my hogfish looking worse. Any suggestion?

BryanM · Apr 28, 2026

add an airstone or two, see if that perks them up, if it does you know the flow is the issue.

And I think it probably is, if the chiller "removed" most of the flow.

Do you have powerheads in the tank? If no, probably need to fix that, get better surface agitation of the water, but airstones are quick cheap, and easy to add immediately and I think you should notice a difference fairly quickly

mushy coral · Apr 28, 2026

BryanM said:
add an airstone or two, see if that perks them up, if it does you know the flow is the issue.

And I think it probably is, if the chiller "removed" most of the flow.

Do you have powerheads in the tank? If no, probably need to fix that, get better surface agitation of the water, but airstones are quick cheap, and easy to add immediately and I think you should notice a difference fairly quickly

I removed the air stone when i added the skimmer in. Today they do come out a bit at noon but when i got home at 7pm the fork tail was sleeping and i cannot find the hogfish anywhere. But right that moment the forktail wokeup and come out swimming so i grab the minced shrimp and feed it, and the hogfish smell food and he cameout too. They both look healthy, no problem swimming and eating alot. Dont really know what made them acting weird but glad they better now. I will do few more rounds of wc and change to a bigger pump for flow.