So, the reason I would like to bring this up, is due to the fact since I first signed on to this site everyone said: DO NOT USE CLEANING SPONGES.
I let my nephew use the 30 gallon (reason for a different size tank in the end is because the tank is too high for him
), and got him a betta fish. My neohew is 10 years old. I made sure to tell him, when he asked if any sponge works, that no it does not because there are chemicals in there that are not good for aquariums and fish.
I did not know what he did right away - I had asked him all sorts of questions as to why the fish looked so pathetic... Even made him up how much food the fish got (he feeds the fish religiously, as he does not want it to die). The fish looked... Sickly. Thin, stiff swimming, not very active, didn't flare as much... He was pathetic looking.
When I emptied the tank when moving it to my place, I noticed the red sponge. RED? Aquarium sponges are not red... And then it hit me, why the fish looked so pathetic. He had put a cleaning sponge in there.
Now, he is going to have to prove to me he REALLY wants the fish. He likes being responsible, feeding the animals, making sure they have water, etc.
I now have the betta in the heated 15 gallon long, and he has gotten 100 times better overall... Appearance and behavior. Nothing really changed, water schedule has always been the same, feeding schedule has always been the same, etc. Only thing different is the fact there is NO cleaning sponge in there.
Use real aquarium sponges to avoid poisoning your fish.
It took this fish a month before displaying symptoms - but in that time he was suffering and no one knew it, or knew why! If I had not moved the tank, left it there, the fish would have surely withered away and died. My nephew will have to go through the basics all over again, before he gets the fish back.