Do certain fish react quicker to CO2 levels? I have a gold nugget pleco that just lay on the bottom on his side and despite proding him he did not move when I had increased the co2 level slightly. I easily netted him out and placed him in another tank without co2 and an air stone and he quickly dashed around the tank and seemed revived quickly. Still have him there and is doing just fine although he makes his home behind the filter tubes. None of the other fish seemed effected at all including corys, loaches, ottos, mollies and swordtails and 3 bn plecos. A couple weeks later it happened again in another tank I had set up with c02 with a bn pleco. Instead of moving him out of the tank I just cut the co2 back a little and he has been fine since too. Both effected plecos really were gasping and showed no movement even when turned over on their back and I really thought both were not going to make it. The drop checkers were hardly showing much co2 content. No other fish in either tank showed any signs of to much co2.