Help! My fish are dying one by one

[Millarar]

Hi! I really need some help... I don't know what to do next. I have a 50 litre tank (I think that is 20 gallons?) and it's 4 months old. It cycled and my fish were fine for a couple of months. Then they started dying one by one. Never more than one fish looks sick at a time. It's like they tag-team dying. First it was my 5 guppies. Then a Cory. Now my blue rams. My water tests 0 for ammonia and nitrates. Nitrates have been up around 40 but my tap water is high so it's hard to keep down. The fish shop tested my water and said the levels were all fine. They have no obvious signs of illness except occasionally one of them shows stringy white poo and clamped fins. Why should I do if water quality ok??

 

[NickAu]

The fish shop tested my water and said the levels were all fine.

Fine means nothing, Most pet shop employees wouldn't know their elbow from their backside.

 

[Millarar]

I have an api master test kit and it says they are fine too...

 

[luca1980]

post the actual results of your test here and we will have a better chance of helping you

 

[Munroco]

He did post them, in the original post. Ammonia and nitrite zero, nitrates about 40ppm which isn't too excessive.

 

[Demeter32]

Clamped fins and white stringy poo usually means internal parasites. Were the fish that died really skinny? Are the other fish eating or spitting out food? How often and how much are you feeding them? Do they every "flash" of objects in the tank as if they were itchy?
Can we perhaps get a few pictures of the current fish, especially of ones that might be acting ill?
I sound so demanding but the more we know the better.

 

[luca1980]

He did post them, in the original post. Ammonia and nitrite zero, nitrates about 40ppm which isn't too excessive.

I was only suggesting he post any additional results as he mentioned that he had an API test kit and everything was fine - suggesting that he had retested the water after the LFS did.

 

[StevenF]

What is the PH? Also test your tap water for PH, ammonia and nitrates. How often do you do a water change and how much.