I bought a used 92 gallon tank the other day. I brought home a little less than half the water. Added the rest of new water from rodi system and my nitrates are very high between 80 and 160 on the chart. I tried 2 different test kits and they were both the same results. The ph is a little low also at 7.8. Amonia is 0 and nitrite is 0. What should I do? I'm assuming keep doing water changes.