I am a SeaChem safe fan, been using for years now, as stated before 70 bucks or so get you 2.2 LBS or 1KG, this will treat up to 200,000g water. same thing as prime but a hell of allot more cost effective. I do an easy 400 to 500g water changes a week. i do not pre mix. empty tank to fin level, measure it in and then fill. have never had an issue with any fish.