Why are my fish dying?

[duanes]

Assuming the test strip is correct, the very dark nitrate patch shows your water change schedule needs to be upped to about 80 %, small tanks like 45s need many more, and much larger water changes because water quality degrades so fast.
A 50% water change every 3 days would not be too much.
And although your tank water appears to test hard...
According to the strip,it has a very low alkalinity (buffering capacity), meaning there is not enough calcium to neutralize all the fish urine, so without much larger and more frequent water changes, your fish are swimming in fish urine soup.
This is also indicated by the low pH, ie acidic (fish pee=pH crash)
The high nitrate in combination, low low alkalinity, is very unhealthy for fish, and none of these are fixed by filtration, only water changes.
Could you post a photo of a test strip using only tap water, to compare?

 

[Fishnerd360]

Well my fish water is making my oldest fish still live, he is about 10+ years old and one of my first fish. A upside down catfish.

 

[Fishnerd360]

This my tap water

 

[Fishnerd360]

I don't think the nitrate test thing works, all my other nitrate test parts are all the same color. I may be wrong about this.

 

[Galantspeedz]

How come your current test all colours different? Especially ph and alkaline

 

[duanes]

I agree seems the nitrate section of the test is bad.
Your tap water looks to have plenty of alkalinity, but the tank water is low, which usually means the fish urine and other metabolism by-products are eating up all the buffering capacity.
The only way to remedy this is more frequent, and larger water changes, filtration will not help. You need enough water changes so that the alkalinity of the tank remains closer to that of the tap, if you do I would imagine your pH won't crash either, and fish health would be better.
I kept a log book of water parameter trends in my tanks, and the trends showed I needed to do 30-40% water changes every other day, to keep my tanks at equilibrium, I had about 1000 gallons of tanks at the time. So to me, doing a 30-40% water change on only a 45 gal every other day would be a breeze.