Same crap I've been using almost a year for mine, just add a cap or 2 every wc cuz a 50% wc will take half the product out. It's some powerful stuff, best way to add it the first time is get a water bottle pour 2 caps in it, fill with water, shake and pour 1/4 of the bottle into the tank, let sit for a minute and if u want darker add another 1/4, that way if u don't need it all u don't waste it. First time I added it I straight poured 30% of the bottle into my tank, needless to say my water was 100% black, couldnt see my fishes at all even with lites on, had to do a 75% wc to get it to a dark brown, man that was rough lol.
I love the stuff and I swear by it.
Good man Afro, following some good advice!
Go S. Vettel #1 rb8