I hope you don't mind me putting it here but I have a simple diafine question too.
Why would you buy a gallon instead of a quart size? If you buy the gallon size, can you store the powder and mix new from it? That would make sense. But if it lasts as long as people say, I don't see why you'd want a gallon of liquid unless you were using really big tanks.
Diafine can last years in glass bottles. Seriously. I'd buy the gallon before the quart because the savings is monumental.
No idea what's going to happen next, but I'm hoping it involves being wrist deep in chemicals come the weekend.