When we first received this product from Germany for testing, we were shocked to realize its similarity with the AZ-NO3TM in terms of usage (although they work totally different in terms of chemical reaction and method). Just like the AZ-NO3TM, this product renders your protein skimmer as an exporter - Phosphate in this case. According to the manufacturer's experiment, it brings down your PO4 level from as high as 3 mg down to 0.5 mg in 24 hours. Depending on your water quality and levels of PO4, some of our experiment indicates a somewhat slower response time - which is about 0.04ppm of PO4-drop / usage of PO4-MinusTM, then on the 5th day, PO4 disappeared all of a sudden. So its de-phosphate effect is not as gradual as AZ-NO3TM 's denitrating effect, but expect an abrupt drop in PO4 on around the 4th - 5th day. Starting PO4 levels in other tanks ranged from 0.15 ppm to 1.6 ppm, and PO4 levels dropped to nearly ZERO as well! Can be used with the Korallin S-Plus Trace Elements to maintain a healthy kH. Extensive testing indicates that it can be used with the AZ-NO3TM as well with no loss in potency in either product! They are best to be used together if you want an extremely low NO3 and PO4 marine environment. This product has been overdosed 10 times in our aquaria for many occasions to show its harmlessness to reef animals. Most of its users in Germany use this product once per week to control the PO4 in their fish-mainly aquaria which require constant and large amount of feeding. $29 for 500-ml size. Directions - Shake well before use. 2 - 5ml for every 100 litres. Take water chemical measurement after 24 hours of treatment. Repeat if necessary. Water may be cloudy for a short time. Watch kH & ORP closely. kH cannot fall below 5. If it does, use Korallin S-Plus Trace Elements, or other kH Buffers.