TW: dead fish(no pics), long post but I want to get all the details I can.
I set up a new 20 gal long tank. Sand substrate, some seiryu stone, java fern, pogostemmons, water sprite, money moneywort, and a sponge filter. Throw some food in the tank as an ammonia source and let it sit to cycle. After about two and a half weeks ammonia and nitrite tests are registering zero. Some algae has started growing on the rocks and substrate also. I wait another week and a half and head to the lfs for fish. I bring a picture of the algae growing because it doesn't look like any I've seen, don't bring a water sample because I thought all was good. LFS employee suggests testing the nitrate before adding fish but otherwise not worried about the algae. Bring home 5 cherry barbs, a nerite snail, and 2 amano shrimp. Test nitrates before adding fish and they are sky high (80-100 ppm). Do a 50% water change and vac out most of the algae, before adding livestock and then add after acclimating them.
Next day test the water and there is ammonia(.25-.5) and nitrite (~.25) registering. Add some Complete conditioner to detoxify the water. Grab a 1oz bottle of turbo start at the store, do another 50% water change, and add the whole bottle of turbo start. Monitor the water for the next few days(levels never register above 0.5 for ammonia or nitrite)adding Complete every 24 hours. Lose 2 of the fish. Day 4 after adding turbo start ammonia and nitrite are registering zero again so I think I'm in the clear. Two days later, lose another fish. Bring a water sample to LFS that weekend. Their test shows a slight amount of nitrite, no ammonia, good nitrate levels. Ask if they think I can add fish back to the group and they say yes so I get 4 more cherry barbs and add to the tank.
Next day another fish dies. Check NH3 and NO2, still register zero. Two days later notice white spots on a couple of the remaining fish.
Remove fish to a 10 gal quarantine tank with 1tbs aquarium salt per 2 gal and a heater to start raising the temperature up to 82/83F. Fish do okay for 2 days but still have white spots. By the end of the third day the remaining fish have passed. No NH3 or NO2 register in the quarantine tank.
Bring a water sample back to LFS, show them the pictures. They claim it's bacterial issue due to water quality. They say thier test show ammonia and nitrite (see pic, I use API test kit, not sure what they use so I don't know what color the test should be). Home API kit test same day as LFS test not registering ammonia or nitrite (unless I'm reading wrong).
I want to figure out what the problem could be so I don't lose more fish. I know there are things I could have done better along the way (test before bringing fish home/bring water sample to the store; not add more fish until I had a better idea why I lost the first ones) so I don't want to continue and lose more. It looks to me like ich. Is it likely ich or bacteria issue due to poor water quality? Or a combination of all these factors over stressing the fish? If you've made it this far thank you for reading.
Snail and amano shrimp are still alive btw.
Other water parameters:
Temp: 74F