ok so i bought a saltwater aquarium from someone. A 75 gal tank with 70 pounds of live rock, protein skimmer. two water jets, and uv sterilizer. he had left the tamk running for a few months with no fish in it just a few hermit crabs. I moved the tank, water, live rock from his house to my house 10 min drive time and set every thing back up in my house only took a few hours. he had let about 10-15% of water evaporate so i added fresh water on the first day to get my specific gravity back. then 5g water change every day for the last 7 days then a 30g water change today. i jsut tested everything my ammonia,nitrite are both 0 ppm my ph is 8.2. my nitrate is 160ppm why!?