Yes. It's inorganic and doesn't leach anything into the water that I know of. Pretty much anything safe for corals and marine fish, which are like you breath on them and they die sensitive, is going to fine for scale-less fish.

Hi Sburg, Not a simple question. It depends on how much phosphate is in the water. The product instructions say: Use 85 mL (1/3 cup) for every 200 L (50 US gallons) saltwater or 400 L (100 US gallons) freshwater. Leave product in place for 4 days, then test phosphate or silicate concentrations. If the concentration of the component you are trying to decrease has not dropped to around 0.02 mg/L, then replace the PhosGuard. Its capacity is as follows: PhosGuard (Alumina Oxide) 0.87 mg/g There isn’t really a straight forward answer…BUT in general, a 250ml (5.3oz) should treat 50 gallons Saltwater pretty well, and about 100 gallons Freshwater pretty well, unless the level of phosphate is overwhelming.” So, 1 package should be enough, but it really depends on the level of phosphate in the water, and how the level is impacted after use and testing. Thanks