trueits a bit of that and chemical reactions within the aquariums dude o organic matter as well though...u cant really test for that.not neccesarily no...algae buildup is usually down to flow issues in the tank...
thats a bit harsh...lets ask more about the fish...is it eating and how long have u had it?she says its fat so it is probably eating i had mine do great when my tank was a 29 gallon and it is still doing wonderful in my 55.get rid of it (by giving back to lfs, dont kill it), they should be in at least 75 gallons that is mature about a year minimum, it will starve in a tank of this size since they require lots of meat like copepods and stuff. Had to say this somewhere before problems start, sorry for being off topic.