Please help. Dying fish

[Quim]

I recently made a DIY aquarium background and since then all my fish have died, except for 3 ghost shrimp. I thought it had something to do with hard water so I bought a test kit for hardness and a softening pillow. I got the hardness down to normal and all my levels were 0 except for nitrate which was 5. Ph was 7.6. And temp was 77. After the levels had been good for a few days I decided to try again. So I got 3 platys to start with. They acted normal for 2 days and were swimming this morning. Then I come home at noon and they are all dead. Please help me. I don't want to kill anymore fish.

 

[Wiggles24]

Can you explain more? How long has this tank been set up? What are your other levels? Additionally plz talk about the DIY background and why it could possibly be the cause.

 

[AlexandraDanielle21]

Just to confirm, ammonia and nitrite at 0? What are you using to test everything, strips are known to give less a accurate results than a liquid testing kit. Also, how was your tank cycled? Planted? No plants? Did you use filter media to cycle or did you cycle with fish. Your water may have been unstable when you added fish, or if your filter had been used before it could be carrying harmful bacteria. And did your fish have any spots, were there find tight to their bodies? If any of them had gashes or common symptoms they could have been carrying a parasite, Or the parasite could be in the water already.

Sorry to bombarde you with questions

 

[Quim]

I found the culprit. I had the tank empty and my bio wheel wasn't running so the bacteria died I guess. So it had to re cycle and I didn't let that happen. My ammonia and nitrite spiked. So I think that is what did it. I have it densely planted and 3 ghost shrimp are still living. I added some bio start and I'll keep checking and doing water changes until it cycles. Thank you for your response though.