The alternate use has any body had any suckses with the adding directly 1 teaspoon for 100 gallons twice weekly? I have done it and mabe im lucky but i dont have to do water changes clean the glass or feed my fish its one big self sustaining ecosystem.
Granted just sayin it has happend to me a 150. The glass was a good inchthick. One from the 60's. I leaned a good 75 pound rock on it. It gave way right at the middle brase didnt loos any fish but when it went i just about had a heart attack
I have leaned rock up against the back of some of my fresh water tanks if it is a big rock watch out if its an old tank sometimes the rock might make the seals seperate