Hi, I just combined my 125 and 75 gallon tanks into a 500 gallon....so really my tanks have been around for years and the only new thing is 300 gallons of new water. anyway, ever since the tank has been set up I have had a nitrate issue. It's been 3-4 weeks now and it started on the lower level of OKAY on the chart. Now its in the lower level of the unsafe zone. Previous advice from other posts were to get a sump. Anyway, I not only have a sump now but a larger tank, 300 lbs of live rock, about 10 reef fish, 1 zebra moray, 1 brownbanded shark, and a huge clean up crew consisting of snails, crabs, cucumbers, star fish, etc. I feed 1 small cube of frozen food daily sometimes skipping a day. any ideas as to why my nitrates are high? Thanks in advance.