Please Help, Why Are My Fish Dying All Of A Sudden

[Ilovemybetta]

So i have a tank, about 5 months old, went threw the nitrogen cycle, my tank is nice and clean, I have 1 guppy(had 2) 5 harlequin rasboras, 2 corys and used to be 1 otocinclus catfish. My oto just recently died and so did my guppy like a week apart, why are they dying. My guppy had a darkish color on his back, and my oto was fatter, paler, and parts of his tail was fallen off. Why is this happing

ammonia:0
Nitite:0
Nitrate:15

What is going on, im starting to freak out thanks

 

[WILDER]

How many gallons or litres is your tank please?
What do you feed your fish?
What type of test kit are you using?

The fish that was fatter, did he look bloated in the tummy area.
What does it look like when your fish go to the toilet. Example. Is there
waste long white, and stringy looking.
Can all your fish maintain balance in the water.

Darkening of colour can be an indication of a problem. Bacterial infection.
Paler in colour can be signs of stress, and ill health.

 

[Ilovemybetta]

I have 20 gallons
I feed my fish Aqueon Flakes also Hakari Bloodworms
I never really pay attention when my fish poop, but last time I remember it was brown

Also it was only pale in a couple spots, the rest was his normal color

Thanks for helping

 

[WILDER]

There is room for improvement in there diet.

To many bloodworms can cause bloating. So only feed them sparingly.

You could introduce some fresh veg into there diet.
Veg like, broc, peas, lettuce, spinach, cabbage, anything green.

Frozen food such as,
brime shrimp.
Daphnia.
You can buy packs of frozen foods with 4 different meal choices.


For now add a few peas to a cup, or jug, of boiling water for a few minutes.
Let them cool down.
Pop out of shell. As fish can't digest the shell of the pea.
Crush into small pieces and add to the tank.

The guppy that looks abit dark in colour, is there also signs of the fish acting listless and lethargic.