QUOTE]Aqualung In my (inexperienced) opinion, it seems like the 33 gal. is way overloaded with fish. [/QUOTE]
I agree. You have/had an arowana, 3 knifefish, 4 eels, 3 plecos, as well as the other fish you mentioned, in a 33 gallon tank...way too small. I don't mean to criticize, I would like to help and hear of your success in this hobby.
Everyone is small now, and I plan on going for a nice big tank in the future when they grow
They are growing now, and should be growing quickly. Large predatory fish generally grow quickly and produce a lot of waste. Plecos are notorious for producing large amounts of waste. Unless you move some of those fish to a new home I am afraid they will not be around when you get a bigger tank.
Think about this when you do buy a larger tank: perhaps you do not have the room/$/time,etc. (right now) to keep all of the fish you would like. Who on these forums does? Be patient and get the absolute largest tank you can, then select which fish you will keep. Or, if you decide you must keep a specific species, revolve your tank/equipment purchases around that/those fish knowing in advance what their adult size will be so you can provide a large enough space for them. I would love to keep an arowana, but I know I do not have the means to care for a four foot predatory fish. I don't mean to lecture, but I am not sure if you have thought about these things. You will be much happier and have much more success if you do.
To solve your problem now, as the others suggested, you need to do large water changes daily. And again, I believe you need to find new homes for some of those fish right now. Good luck and keep us posted. I really hope this works out for you.