Guppies in rough shape

[Marnol D]

Hello,

Two of my female guppies are looking rough. They have developed an arched back and have lost their color (they are almost 3 inch long guppies my largest who was over 3 inches passed away yesterday and had the same issues). My tank cycle crashed recently so that could be the issue and they haven't recovered yet. The parameters now are 0 ammonia 0 nitrite 20-30 nitrate with a ph of 7.8 (mineral additives from equilibrium keep the tank mineralized this has been a very recent thing i have started doing to try and help the fish ,however since i've started doing this the other guppies seem to be healthier being more active and colorful) temperature is 78F. A week and a half ago (when  noticed the water turning cloudy) I tested the water and it was less than .2 ammonia and around .25 nitrite but has since established back to 0s . Its been maybe 3 days since the tank has cleared up from the bacteria bloom and looks to have stabilized. The fish have regained some colors but still look weak ,however they are being slightly more active now. Should I give it more time to see if they bounce back or is there something else I can do for them?

[RovingGinger]

You could add some salt if your tank is not planted (and honestly so far a small amount of salt has not hurt plants when I’ve added it - under 1 tsp per gallon has still seemingly helped fish and not killed plants). 
 

How old are the females?

[Marnol D]

30 minutes ago, RovingGinger said:

You could add some salt if your tank is not planted (and honestly so far a small amount of salt has not hurt plants when I’ve added it - under 1 tsp per gallon has still seemingly helped fish and not killed plants). 
 

How old are the females?

 females about ~4-5months maybe. I have salts in the tank and the plants havent had any negative reactions yet.