My fish are dying slowly, one by one???

Hey, I have a 60 gallon aquarium with two assassin snails, three swordtails, three mollies, four albino cories, one hatchetfish, and six harlequin rasboras. I used to have nine rasboras and six cories. They all have slowly started dying and don't get why. My water parameters are as shown; Ph - 8.2 Ammonia - 0ppm Nitrite - 0ppm Nitrate - 20ppm

The tank was cycled with TTS, and I added fish slowly. I would like to mention I had more swordtails, but those died... I really didn't know the cause of their deaths. They sit in the front hall of our house, having not much activity except SOME light which only hits the corner of the tank. I feed them every other day, and they all eat. I want to say something about the hatchet, that being that I have hunted for them ALL around my city and the cities around my area. None of the pet stores have them, so we decided to order them. We hope to get the hatchetfish a small shoal, but I really want to figure out what's happening with my tank. If anyone could help that would be appreciated. I can give additional info if needed/requested. Thanks

 

One last thing, I would like to say that two of the rasboras were found on the filter, and one on the bottom. The cories were found resting on the sand.

 

How long have you had your tank and fish?

 

I got the tank in the beginning of summer, very early june. The rasboras have been in the tank for about a week and a half, maybe two weeks. The swordtails have been in there for about a month, the cories, mollies, and hatchet were in there the first few weeks.

How long have you had your tank and fish?

 

This is just a theory, please forgive me, but could it be possible they aren't getting enough food? I'm just asking because your parameters are nice.

 

On the opposite side (sorry) are you over feeding and could food be rotting at the bottom?

 

I try to prevent overfeeding by feeding every other day, but maybe I still am somehow overfeeding them? I have been doing my weekly water changes

On the opposite side (sorry) are you over feeding and could food be rotting at the bottom?

 

It could be, as I DO feed every other day, but I don't think that that would actually starve them. They are eating still after about 10 minutes, from small pellets that sink to the bottom and they pick at them but I only put a few.

This is just a theory, please forgive me, but could it be possible they aren't getting enough food? I'm just asking because your parameters are nice.

 

Could it be the temperature in the tank? I note that you mentioned some light "hits the corner of the tank". Is this sunlight? Heat? Also, what is your substrate? Could the bottom feeder food be falling into gravel so they can't reach it? I feed my cories rather large sinking wafers, every other night, plus they get whatever flakes drop to the bottom of each morning feeding of the other fish and brine shrimp once each week. They are doing fine. In fact, they have spawned (7 fry have lived and thrived).. Perhaps you could try Marineland Shrimp Wafers and be sure they stay above the substrate; feed at night so the other fish are less likely to eat them.

 

Did they show any symptoms before dying? Gasping, raised scales, torn fins, loss of appetite, abnormal poo, swim bladder problems, etc?

Unlikely that they're not getting enough food, fish can survive on very little food.

 

I checked my temperature, and it may be heat... It is sunlight, but the thermometer is in the corner where the sunlight hits, and its currently at about 78F. It could be a possibility that it does heat up more during the hours of sunlight? I have a black sand, specifically National Geographic black aquarium sand... The cories are eating some shrimp pellets, which they love from what I see. They go and eat that, and go crazy when I feed them! Back on topic though, they are eating so I am not entirely sure. :/

Could it be the temperature in the tank? I note that you mentioned some light "hits the corner of the tank". Is this sunlight? Heat? Also, what is your substrate? Could the bottom feeder food be falling into gravel so they can't reach it? I feed my cories rather large sinking wafers, every other night, plus they get whatever flakes drop to the bottom of each morning feeding of the other fish and brine shrimp once each week. They are doing fine. In fact, they have spawned (7 fry have lived and thrived).. Perhaps you could try Marineland Shrimp Wafers and be sure they stay above the substrate; feed at night so the other fish are less likely to eat them.

 

I really didn't see anything wrong with them, the rasboras schooled, the cories would chill, swim every so often, just what they normally do. What I did notice, was that one of the cories I found dead had small fin nips, which worries me. I feel the mollies COULD have done it, as they are very curious and like exploring, and checking things out. It may be an issue like that, but I don't get that mollies would be killing my fish, I thought they were community safe...The rasboras were found on the filter intake, so I am wondering if they get stuck on the filter overnight, but it doesn't make too much sense as it hasnt happened with the hatchet.

Did they show any symptoms before dying? Gasping, raised scales, torn fins, loss of appetite, abnormal poo, swim bladder problems, etc?

Unlikely that they're not getting enough food, fish can survive on very little food.

 

I may have an idea, that I forgot to mention. I have live plants in there, but not too many. My amazon swords and some other plant, that I forgot what was called but will be posting a photo. The plants were recommended by a LFS, that is somewhat like a warehouse and has a large variety of plants. Anyways, these plants have been somewhat browning, which worries me. I don't know if that will cause such a major issue, but they somewhat break off and I have to remove them from floating around. I just wanted to say that just in case that's the issue...

 

Plants melt when you get them. It's normal as long as you don't let the decaying matter mess with your parameters. (Clearly not the case with your test showing good levels.)

 

Just a question about the melting plants, do I take off the part that's melting, or the whole leave and stem.

Plants melt when you get them. It's normal as long as you don't let the decaying matter mess with your parameters. (Clearly not the case with your test showing good levels.)

 

I cut off anything once it starts looking like it's broken and only attached with a thread. My leaves seem to decompose in the middle so they turn kind of clear and I cut off anything clear or brown or black. I leave yellow alone since it sometimes recovers that part. Be careful that whatever you bury in the substrate isn't also decomposing. A little will be handled by your bb just fine. A lot will cause a spike.

 

I really didn't see anything wrong with them, the rasboras schooled, the cories would chill, swim every so often, just what they normally do. What I did notice, was that one of the cories I found dead had small fin nips, which worries me. I feel the mollies COULD have done it, as they are very curious and like exploring, and checking things out. It may be an issue like that, but I don't get that mollies would be killing my fish, I thought they were community safe...The rasboras were found on the filter intake, so I am wondering if they get stuck on the filter overnight, but it doesn't make too much sense as it hasnt happened with the hatchet.

I don't think the mollies did it either, they're not aggressive fish. Strong, healthy fish are able to swim away from the filter, so there must have been something wrong with them.

Can you post pictures of your tank and remaining fish?

 

Sure, ill get some photos and maybe a video later. Its somewhat empty, and my first large tank so please excuse the emptyness in the middle

I don't think the mollies did it either, they're not aggressive fish. Strong, healthy fish are able to swim away from the filter, so there must have been something wrong with them.

Can you post pictures of your tank and remaining fish?