Dont forget to test the water that you are putting in the tank. You may have nitrates in the water you are adding to the tank. I had a similar problem with nitrates. I could never get it to zero. I took all the crushed coral out, replaced it with aragamax. I also had to purchase a ro
setup to purify my tap water. Since these changes, I have had zero nitrates for quite some time.
55 gallon, FOWLR, 70 pds of live rock, live sand, HOB Emperor 400, protein skimmer, 2 maxi jet 1200. T5 lighting, 1 snowflake eel, 1 spotted cardinal, 1 6 line wrasse, 1 foxface one spot, 1 female percula, 1 anemone, snails, crabs,