15 Gallon Tank Corydoras keep dying of unknown illness!! Need help!!

Awesomeneptune

Hi,
So I have a 15 gallon (57litre) fish tank with 1 male betta and 2 Corydoras. My Cory's have been dying.

I first started the tank with a betta and 3 Cory's but then one died, It looked as if it had been I'll when I first got it and my other fish seemed fine so I didn't treat the tank. I got 2 more Cory's to add to my tank and they all got along fine. Then a few months later another Cory died, showing the same symptoms as the first ( lack of movement, swimming on side and in circles, gasping for breath). This time I knew something was wrong so I treated the whole tank with fluke solve. I thought it was all going perfectly until this morning ( almost half a year since the last death) when I woke up to 1 of my Cory's being dead. This one had a bloated belly and a bit that looked quite red and sore underneath it's 2 bottom fins. It showed no other symptoms before hand apart from I noticed it was glass serfing closer to the top of the tank last night, like my previous I'll corys had. One of my remaining Cory's is looking quiet bloated too.

I've now only got 2 Cory's and the betta in the tank. I was planning on buying them a larger tank but I don't want to until I have treated them all for whatever this is. I think it might sound a bit like dropsy? But it's quite hard to tell as the Cory's are scalelss. Do the Cory's deaths seem connected? Any advice on medications to treat them with ( preferably snail safe) would be really appreciated, thank you!

Forgot to mention I also take out 1/3 of the water when doing a weekly water change, if you need any other imfornation let me know, thanks again.
 

FishDin

Did you cycle your aquarium prior to adding fish, and do you know the current water parameters (ammonia, nitrite, nitrate, pH)?
 

Awesomeneptune

I did cycle my tank before adding my fish and here are my water parameters:
Nitrite:0
Nitrate: 0-10 ( I'm not sure that bit of the test strip is very accurate as it never changes color)
Ammonia: 0
Chlorine: 0
Ph: 6.7
Gh: 4.2dh
 

Fisch

What kind of filter do you have in that tank, any aeration? What is the temp in the tank and what kind of Cory?
Are you 100% sure the Betta is not harrassing the Cory?
 

Awesomeneptune

What kind of filter do you have in that tank, any aeration? What is the temp in the tank and what kind of Cory?
Are you 100% sure the Betta is not harrassing the Cory?
It is a sponge filter and I also have an air stone in it too. They were all fake Juli Cory's (not 100% sure what type as they were sold as Julis). I suppose the betta may have chased the Cory's a bit but I've never seen him actually hurt or touch them. He also occasionally flares at them ( I always stop him when I see him doing it by lifting the lid of the tank up) but as I said he hasn't injured them at all
 

Fisch

Temperature? The Cory upper temp is the lower comfort temp for a Betta. I am doubting that Bettas are trainable by connecting their flaring with the lid clapping, except that it may cause additional stress to Betta and Cory.
I myself would increase my frequency of water change to daily to eliminate water quality, then not replace the Cory at this time, but look a a snail as alternative.
 

Awesomeneptune

Temperature? The Cory upper temp is the lower comfort temp for a Betta. I am doubting that Bettas are trainable by connecting their flaring with the lid clapping, except that it may cause additional stress to Betta and Cory.
I myself would increase my frequency of water change to daily to eliminate water quality, then not replace the Cory at this time, but look a a snail as alternative.
I do not clap the lid I just open it up a bit as my betta always comes to the top. The temperature is 26c. I'll try increasing my water changes and I'm not going to replace the Cory, ive also already got 3 nitrite snails in the tank so probably won't get another just incase they introduce any new illnesses. Thanks for your help!

Also would it be worth getting some stress coat. As if I'm doing more water changes it might stress my fish out and I've heard stress coat is meant to help (I'm not sure how true it actually is though). Would it do any good?
 

Fisch

Stress Guard would definitely not hurt.
Another question, what do you feed?
 

Awesomeneptune

Stress Guard would definitely not hurt.
Another question, what do you feed?
My betta gets 3 ocean nutrition betta pellets or bug bites ( occasionaly some frozen food) each day. My Cory's get either bug bites or king British catfish pellets each day.

Also I think in the UK the name for stress guard might be different, is API stress guard the aloe Vera one or the one with the bacteria? I think it's the one with aloe Vera in but just checking!
 

Fisch

I am not familiar with the API product as I use Seachem Stress-Guard, and I do not see the Aloe Vera ingredient.
In regards to food you may want to try some additional variety. As humans on the same processed food every day, I also believe that there is a nutrient insufficiency when feeding fish the same food day in day out. Try to let some frozen food sink to the bottom, I soak my community fish food and let it sink, then Omega One Shrimp pellets, Hikari sinking wafers, API bottom feeder wafers, Bug Bites. And a day of diet here and there is not bad neither. Fish are opportunists.
 

Awesomeneptune

I am not familiar with the API product as I use Seachem Stress-Guard, and I do not see the Aloe Vera ingredient.
In regards to food you may want to try some additional variety. As humans on the same processed food every day, I also believe that there is a nutrient insufficiency when feeding fish the same food day in day out. Try to let some frozen food sink to the bottom, I soak my community fish food and let it sink, then Omega One Shrimp pellets, Hikari sinking wafers, API bottom feeder wafers, Bug Bites. And a day of diet here and there is not bad neither. Fish are opportunists.
Thank you! I do have some shrimp and algae wafers but on the times I've tried to feed them to my Cory's my betta has just got them in his mouth and swam about the tank with them! I'll try getting some more variety soon!
 

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