Substate killing fish? Possible disease?
I have a 20 gallong long tank. The inhabitants are as follows:
2 scralet badis
2 danio margaritus
3 leapard danio
1 zebra danio
2 kyathit danio
5 khuli loaches
3 hillstream loaches
6 amano shrimp
I understand its a little over stocked, but i have multiple aquaclear 20 filters with extra ceramic rings added and the carbon filters removed. I have a power head rated for 30-50 gallons for extra current and surface agitation. I keep the water at 74 degrees.
I also have a lot of plants including: multiple types of anubias and java ferns, riccia, s. repens, java moss, water sprite, bacopa, a mossball, dwarf baby tears, alternanthera reineckii, banana plant, and some cryptocoryne.
Now, to get to the problem. I had the whole tank set up with some soil under some sand as substrate for about 6 months and all of the fish were in good health as far as i could tell. I got tired of the loaches digging up dirt, so i decided to pull everything out of my tank and add some caribsea eco complete substrate instead of the soil and sand about 3 weeks ago.
I removed all the fish, then plants, and hardscape. I cleaned the tank, and added the eco complete as directed. I put 2x 20lb bags in my aquarium. I chose eco complete because it is advertised as ready to use and doesn't need to be rinsed. I didn't want to waste time rinsing soil while my fish were in a bucket with no circulation.
I added the hardscape and replanted my tank, filled it with water, and added my fish. The water was a little bit milky/ cloudy white, but i figured that was normal.
Over the next few days all 3 of my hillstream loaches and 2 of my amano shrimp passed away. They were very pale and at the bottom of the tank. I did an amonia test and it read 0. I also did an API 5 in 1 test fo ph, kh, gh, nitrite, and nitrate. The ph was 7.0, gh was 30ppm and kh 40ppm, nitrite was 0, and nitrate was barely detectable. I have also been doing flourish comprehensive fertilizer after every water change and flourish excel daily. I have used flourish iron a few times sparingly as well. All in all, the same fertilizer regiment as before swapping the substrate.
Surprised by this, I put carbon back into one of my filters. After a week or two of no fish deaths, i added 2 more hillstream loaches. One of them died a few days later. Again I did water tests that all came out normal. Today, i found my Zebra danio floating at the top of the tank. He was pale in color and with rigid fins.
The only idea I can come up with is that there is something wrong with my eco complete that doesn't show up with my test kit, or i have some sort of disease. I have been doing 50% water changes every 5 days.
Can somebody please help me?