I have a 55 gallon tank with a 20 gallon sump 2 clowns, 2 cardinals, a wrasse and a goby. Several clean up crew. My issue is that I have zero or very low phos and high nitrate reading 75 on the Hannah reader I have been vinegar dosing and doing water changes wondering if my issue is actually no phosphates. Any suggestions what I can do to regulate chemistry. Currently running a octo skimmer on the system