Q: How do I use PhosGuard? How long does it work and when is it exhausted?
A: PhosGuard is best used in smaller quantities and changed frequently. In an environment with an excessively high phosphate reading, PhosGuard will exhaust rapidly (4 – 5 days). Place the product in a high flow rate area and test your phosphate levels, changing as needed. When you see that your level is below 0.2 ppm
/L) leave that portion of PhosGuard in the filter. PhosGuard may yellow somewhat as it picks up organics, but that is not an indicator of exhaustion for phosphate removal. Continue to test weekly for phosphate until you see it begin to rise again. You will then know that it is time to change the PhosGuard. If you have low levels of phosphate the PhosGuard will absorb the silicate in your system. It’s inert and safe to leave in your filter.
TL;DR-check levels every few days and replace as needed. This will require a test kit. I know Mr Aqua on Fillmore will help test levels, even if his focus is saltwater. Sage @ Seascapes may, too. I do recommend getting a kit when you can, though, because you'll be using it and it's really more convenient than getting a sample and driving to the shop every few days