Certain Fish dying

[Bigge_al]

I have had my tank set up for over 6 weeks. It is a 44g pentagon tall tank. I am running two 40g filters and two 18 inch air walls.
My readings are:
pH-7.4
Ammo-0
Nitrite-0
Nitrate-20

Gravel subtrate
Current stock;
5 glofish First fish I added
1 zebra danio Added 2 days after
3 platies added 3 days later after danio
All these fish are still alive and well

I have added
5 tiger barbs (3 died or I returned the rest)
Up 7 Mollies (I would have 3 one would die I would replace but not more than 3 at a time.)
6 neon tetras (5 died)
3 Black skirt tetras (all alive and well)

I am losing fish.
The neon tetras would be fine then I would find one dead.
The mollies would be fine then they started getting jumpy and running into things in the tank when being feed and go belly up then recover only a day or two later I would find them dead. I noticed heavy breathing then I added Prime thinking some kinda poison and they calmed down.
I have lost in the past 3 day 3 neon tetras and 1 dalmatian molly
In the tank now:
1 neon tetra
3 black skirt tetras
5 glofish
1 zebra danio
3 mickey mouse platies
3 mollies(1 black, 1 silver, and 1 dalmatian) (Silver and Dalmatian acting funny hovering but the Black one is fine.)
1 albino bristlenose
1 Swordtail


I have not noticed any strange poop, colors.

I feel that if it was food then other fish would die but he glofish, black skirts and platies seem fine.

 

[LyndaB]

It's possible that you got unhealthy stock at the store. Neons are extremely fragile due to overbreeding.

Did you get all the fish at the same store?

Your tank is also very new. Some fish are not as hardy as others and do best in an established tank (6 months or over).

 

[Bigge_al]

As expected both the dalmatian and silver molly died. The neon still looks good. I did not get the mollies from the same place some came from Petsmart, some from Petco, and 1 came from Walmart. I have one black molly left I will just have to wait and see.
I took my water to a Aquarium store not a chain store and they tested to and found nothing wrong with it, They had no clue to why only the molly and neon and tiger barbs died.

 

[LyndaB]

Did they use strips or a liquid test kit?

The strips are worthless.

You should get yourself an API master kit (liquid), about $23 on-line.

 

[gallowchris]

Just from a quick glance, seems as though you over loaded the tank before the cycle completed. That is way to many fish for the age of the tank. 6 weeks isnt a long time at all, your going to have issues with the balance of chem

 

[Bigge_al]

They also use the API test kit that is why I went to them I wanted someone that did the test right.

As far as to many fish maybe but what would that have to do with my fish killing themselves. My test show that all my result are excellent and have been for 4 weeks. I was told that the reason for the fish killing themselves was because of too many water changes stressing themselves out. But this does not explain why only the mollies are killing themselves.
pH 7.4
ammo-0
nitrites-0
nitrates-20

Did they use strips or a liquid test kit?

The strips are worthless.

You should get yourself an API master kit (liquid), about $23 on-line.

 

[LyndaB]

If it's just one species, it really sounds like bad stock from the store.