My po4 is about 4-5ppm . How do I lowers this? All other readings are perfect . No fish in tank just janitors and 2 candy striped shrimp, plenty of LR, and skimmer. Only use RO water and tested the water and salt for po4 with 0ppm results in both. I have heard a lot of different ways to treat just want to hear some of your ways. Thanks in Advance for the help !!