I have a 6 gal freshwater tank, it had 8 fish in it for 7 months. One small neon died. Some were showing stress with blood spots. I thought they were nipping at each other b/c I was underfeeding them (feeding once a day, sometimes twice). Frequently added salt. I did a 20% water change and bought 3 more fish, then all of a sudden my fish started dying. Nitrates were high and I lost all but 3 fish. My dealer (Petco) said I shouldn’t feed flakes, I should feed blood worms and brine shrimp or something. Tried that and fish didn’t eat it. I did another water change to get the nitrates normal. Then I lost the last 3. This all happened within a week. I tested the water with strips after they died. Nitrates were safe but pH and ammonia was too low. Where did I go wrong? I feel like I get mixed information from Petco all the time!! Now that my tank doesn’t have any more fish what should I do? The water is still flowing. Should I do a 80% change, wait 4-6 days, add 2-3 fish & start again?