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Hello,

I have a 60lt heated aquarium with a filter, a betta, shrimps and snails. There are real plants in the aquarium.

A month ago i bought 2 corys. One cory died after 2 weeks, so i assumed that maybe there was something wrong with that fish. So i went back to the pet shop last week on Saturday and i bought 2 more cories and 2 more fish that i do not know their names (but they are dark green with white spots and orange fins. They go always together and they move all the time quite fast. Very difficult to make fotos), because the cory that was alive can not stay alone. I read that they need to be always in groups. But i see that also the two new cories are not acting ok and one (Suzi) moves really slow, when it moves, cause it is mostly on the bottom or on the plants, while the old one (from the first 2 that i bought) is moving all the time and quickly also!

On Sunday i vacuumed part of my gravel and changed the water, something like 20% after 3 weeks, that i didn't do it and most of my shrimps died. Suzi, my cory that is not ok, was already not moving quickly since Saturday that i bought her. My Betta and the two fish are doing fine but the cories no and as already written most of my shrimps died.

My water:
NH4 is <0,05 mg/l (ppm) (test JBL NH4)
NO3 mg/l Nitrat mg/l: 50
NO2: ok
Total Harness> 21o d (1 o TH=1,78 o TH=1,253 o e= 17,8 o ppm)
Carbonate Harness: 15 o d (1 o CH=1,78 o TAC= 21,8 ppm)
ph 7,6
Cl2 mg2/l : 0,8

The conditions were from the beginning more or less like this. So nothing changed. But still i do not know if they are ok.

Before i put the water in the aquarium i leave it in a pot for 24 hours for the chlor to go away and then i add in the water aqua safe.

I feed them with flakes (Tetramin) 5 times a week and Sera Bloodworms twice a week, always in the morning. I put first the food of the Betta and then i soak more food and i put it inside, so that it goes to the surface and the rest of the fish can eat from the bottom.

Could it be that the cories are not fed correctly? I read that they need sand and i have gravel. But also in the pet shop they were with gravel.

Is it just that in my aquarium cories can not live? Should i just stop trying or am i doing something wrong that i can fix?

Thank you,
Natasa