I know it's hard but I would take most the fish back to the store and start getting the tank running properly. The tank is only big enough for a male jack dempsey and several females really. Maybe 1 pleco.
Also when you wash your filter only do this in tank water or a bucket of water that's the same temperature that has been treated with aqua safe or you will crash your cycle again.
Cycle works like this...
Fish waste (ammonia)- then beneficial bacteria turns it to nitrite- then more bacteria turn it to nitrate.
This happens straight away if you have enough bacteria in your filter and enough water turning over.
It's called cycled when you have enough bacteria.
If your reading any nitrite or ammonia your not cycled or are going through a mini cycle from adding too many fish too fast. The amount of bacteria is equal to the fish that sustain it..
Good luck anyway mate, first class in fish keeping over!-)
The mariae will not quite double that size it is now.
I also agree with justarn, since your tank is only been set up about 1 month, unless you used seasoned media, it isn't fully cycled, and if you keep adding more and more fish, it is guaranteed to crash, and the most sensitive fish will surely die first, and agree there are already too many.
A newly set up tank should only start with a few small fish until there is no detectable trace of nitrite or ammonia.