That’s loaded question… people tend to promote what worked for them. I have used both Pond Armor and Sanitred… neither were particularly cheap. I spent about $1300 on Pond Armor, never got it to work for my application. Sanitred worked for me with no issue. You’ll hear other folks tout Pond Armor as the greatest thing out there. I personally tout the Sanitred.
Going into a DIY on a budget, just know that you might wind up with a ruined plywood box if things don’t work out. If I was really budget minded I think going with a pond liner might be a better option as there is only one risk factor and that is if you’re going to seal a window onto your build. (regarding sealing..structural integrity is another risk factor) Using any sealant type product, every square inch is a liability.
Long story short, you’re gonna spend probably close to a grand on wood and sealant for something that big and the build will be a gamble like any DIY tank is. Basically, a 600 gallon build is at the threshold where there is a very good chance that you’ll end up spending more than a nice used factory 700 gallon would cost and the whole thing is a risk where if done wrong could be a complete loss. I guess I’m saying that going into this with a mind set to save money can sometimes backfire, not trying to discourage anyone.
