Originally Posted by InvertPlanet
you need more surface agitation... that oily sum is restricting the gas exchange which happens at the surface and is caused by protein build up.
What is the SG of the tank? If it is high enough you might consider a skimmer, but usually a sponge filter or a hang on the back filter will produce enough agitation to break it up.
BTW... 25 gals for 4 puffers is a tad small ;)
I know it's a bit small but I was mis-sold them when I bought them knowing nothing really about them, the LFS told me I could keep 4 in a 38 litre tank!!!! Once I realised there was more to keeping fish than just plonking them in a tank I started to investigate it and found this site. You guys all taught me about cycling my un-cycled tank and with loads of water changes I got my puffers through the cycle and learnt masses about fish keeping and F8's. I love my fishies dearly and do everything I can to take excellent care of them but I just don't have the room for a bigger tank in my tiny house. I don't want to rehome them as i worry they'd go to a bad home and I love them to bits as they all have different personalities, therefore I make sure they have plenty of things to investigate in their tank, rearrange it regularily and try to enrich their lives as much as possible, I am also very particular about checking levels in my tank. I hope they have a lovely life in their smaller tank with me than they would if I sold them to someone who doesn't really care.