Also, not to nit pick...I know you said a tank was all you could afford, but TRY to get him a wire cage. It will help IMMENSELY. Because even with the tank topper, ammonia is still building up and trapping itself on the walls on the tank. Ammonia and myco don't mix at all. If it's just him, he doesn't need anything enormous. You can even build your own cage if you're crafty enough. I have several I've built myself (I've been breeding rats for 3 years) and it's fairly easy.
"Ma'ii is always out there, waiting. And Ma'ii is always hungry." - Navajo proverb