I gave a 30 gallon tank with one big convict, i adopted the tank after my nephew refused to take care of it of 2 years ago i took control of it, it had cheap national geographic sand substrate, fake decor, I am going to redo it soon with rocks and drift wood maybe cichlid substrate from Caribsea, but nothing I do gets rid of the diatoms, I do 30% weekly on that tank, but I was just curious if it could be the very old t8 bulb?