I have a 10 gal salt water tank, 5 lbs of live rock, live sand, 4 hermit crabs, 2 clownfish, 1 green damsel, ph is around 8.1, ammonia/nitrite 0, nitrate between 0 to 5 ppm. Had a slug, snail, dragonate, 3 other damsels all died in the tank. I change about 3 gallons of water per month, filter...