Corys Dying, Please Help

[FreshwaterAfishianado]

Hi everyone, I'm fairly new to fishkeeping, I've have a 20 US gal. tank running for about 6 months now and I thought I was doing fairly well. I even managed to get my Platys to produce some fry. When I first stocked my tank I had 2 wagtail platys, a sunburst male and a red female, ans I had 3 Glofish danios. The Glofish died within about a month from ich, but my platys have thrived since so I decided to try to add a few more fish. I currently have the two original wagtails, a new blue platy female, four platy fry and 2 snails. I tried to add 4 corys and within 2 days 2 of them stopped eating or even moving at all and became very pale beforethey died. The local pet store has a healthy fish guarantee, and they tested my water for me all came back fine. Ammonia and nitrate undetectable and nitrates barely detectable but definitely <.25 ppm. I keep my aquarium at a constant 78° F. And have never added any salt to it. If anyone can help me solve this it would be greatly appreciated.

 

[Blondielovesfish]

Have you cycled your tank?

 

[FreshwaterAfishianado]

Have you cycled your tank?

Yes, I did a fish less cycle and let my tank run for a full month when I first bought it before I ever bought any fish, do I need to cycle it more than once? I thought that was a one-time thing. I'm maintaining it right now with monthly 25% water changes/gravel vacuums and monthly carbon filter changes

 

[Blondielovesfish]

You should be doing about 20% water changes weekly.
Did you get the actual results or did they just say "its okay" without you seeing the results?

 

[attibones]

When you say you ran the tank for a month, did you add ammonia daily? Or did you just turn on the filter and let it run for a month?

In the meantime, while we try to help you figure this out, do a fifty percent water change. Get yourself a good test kit. Nearly all of us use the API master test kit. You'll also need to have a look at the fish themselves. When you bought them, how did they act? How were they acting at the fish store? While in the store, did you notice any other sick/dying/dead fish in the same tank with your new fish? How large is your gravel? Is your gravel sharp edged? Are any other fish displaying any symptoms? What do the corpses look like?

 

[FreshwaterAfishianado]

They didn't actually show me the tests, no. Should I buy a kit and test myself? Also after you mentioned cycling I looked for a thread on it and I didn't do anything close to that with the bottled ammonia. I used the chemicals and directions that came with my aquarium, a few chemicals called stress zym and stress coat. Then after about a month of it running did a water change and took a water sample to the store.

When you say you ran the tank for a month, did you add ammonia daily? Or did you just turn on the filter and let it run for a month?
In the meantime, while we try to help you figure this out, do a fifty percent water change. Get yourself a good test kit. Nearly all of us use the API master test kit. You'll also need to have a look at the fish themselves. When you bought them, how did they act? How were they acting at the fish store? While in the store, did you notice any other sick/dying/dead fish in the same tank with your new fish? How large is your gravel? Is your gravel sharp edged? Are any other fish displaying any symptoms? What do the corpses look like?

When I first got the tank I used the chemicals and instructions that came with it, I wasn't aware of the ammonia cycling. I thought that the chemicals I had and allowing it to run was cycling. The gravel in my tank is about 1/8" and smooth edged. When I first bought the foxy they were very active and lively, I couldn't see any obvious signs of disease in the store either, all of heir fish very active with fins up andgod color. The dead Cory I have became very pale soon before dying, and none of my other fish seem affected. Even the remaining 2 corys are fairly active

 

[attibones]

Your tank probably isn't cycled yet, depending on how long it has been running. A fish-in cycle takes a lot longer than a fishless cycle. Your LFS probably used strip tests, which are inaccurate. Get a liquid test kit. These a far more accurate. I use stress coat to dechlorinate my water. I really like it. A lot of people also recommend Seachem Prime. The Stress Zyme is bottled bacteria, which does not usually seem to be effective.

Do your fifty percent water change, get the test kit, and keep a close eye on your water. Any ammonia above zero can be Toxic. Any nitrite above zero can be toxic. You'll need to do frequent water changes.

Also, corydoras species prefer sand, which is why I ask about the gravel. They can do well enough on smaller gravel, as they like to sift through substrate. This is also the reason why they need smooth gravel. Your gravel may be small enough for them. I was worried that maybe the barbels had been injured or a piece of gravel got stuck in a gill.

How long have you had the Cory exactly?

What do you feed them?

 

[FreshwaterAfishianado]

I've had the tank running for about 6 months with nothing but 2 platys in it, they had fry about 2 weeks ago, 4 are still alive (she gave birth while we were out of town) the Cory's have only been in for about 4 days. I really appreciate the help, I'll do the water changes and definitely make sure to do my own tests instead of trusting the stores. How difficult would it be to change my substrate to sand? I've been feeding the adult fish tropical flakes in small amounts twice a day, with frozen blood worms every few days. The fry get frozen Cyclops twice a day and I have some shrimp pellets for the Cory, I've only sprinkled those in once in he 4 days though.

 

[FreshwaterAfishianado]

Oh and I also added a female blue platy when I bought the corys

 

[Blondielovesfish]

For changing the substrate to sand it shouldn't be too hard. Buy the sand. You can either buy aquarium sand or play sand. (I'm not sure what brands are recommended for the play sand so hopefully someone else will be able to advise you).
Take all of your gravel out and put it in a bag and then either throw it out or keep it. 
The sand will likely make the tank quite cloudy so before you put it in the tank make sure to give it a good clean by running lots of water through it to get rid of all of the small sand particles that make your tank cloudy.
 
Since your tank has been running for about 6 months I would expect it to be fully cycled even though you didn't intentionally cycle it.
 
For the food shrimp pellets are fine although you would want to be feeding daily. I read somewhere that a good ratio of pellets to fish is 2 pellets per Cory. You may also want to feed some algae wafers that I think most people feed every second day. (whether or not they feed them with the shrimp pellets I don't know sorry).
I think there are some vegetables that you can feed them as well but I'm not sure sorry.
 
Hope this helps!

 

[FreshwaterAfishianado]

Thank you all for your help, I'll be sure to post an update in a few days after I try these things, hopefully I can keep my remaining corys alive and healthy and be able to give them some more friends once my water is safer.

 

[Blondielovesfish]

I hope all goes well!

 

[RCA]

Some posts that may assist you:
 
Is It Easy To Change From Gravel To Sand
 
Gravel Or Sand
 
Not Another Thread About... Gravel To Sand
 
Which Do You Like Better, Sand Or Gravel
 
Unipac Gravel And Sand, Which Do You Own?

 

[FreshwaterAfishianado]

Update: So I've got myself an API master test kit and have been testing my aquarium water twice a day. I did a 50% water change the day after the first post. I added some BioMax to my filter and started dosing with sea hem stability live bacteria.Ive also cut the feeding to once a day. My PH is stable at ~7.5 Ammonia detectable only in trace amounts, nitrite and nitrate u detectable. I purchased some sand to swap with my gravel but haven't put it in yet. I only have 1 Cory cat left but he is very lively and eating like a pig. Here in about a week if he's still doing well I will add a few buddies for him.

 

[This Old Spouse]

Have you cycled your tank?

Yes, I did a fish less cycle and let my tank run for a full month when I first bought it before I ever bought any fish, do I need to cycle it more than once? I thought that was a one-time thing. I'm maintaining it right now with monthly 25% water changes/gravel vacuums and monthly carbon filter changes

 
If you're actually changing all the media in your filter every month, you're starting your cycle all over again, every time you do that. The media in the filter houses beneficial bacteria that eats ammonia and nitrite (it's more complicated, but just for example) which is deadly to your fish.
 
I suggest getting a sponge for the filter media, and don't use any carbon, which is used to removed medication from the tank at the end of the dosing period. Carbon is basically useless after a week or so. Once you get the sponge in your filter, you'll need to start doing daily water changes of at least 50% to keep the levels of ammonia and nitrite as close to 0 as possible. A lot of work, yes. Well worth it, yes. Once your tank is cycled you should only need to do weekly water changes of 20%, 50% once a month. Then when you clean the filter media, you can just swish the sponge around in the used tank water and return to the filter. It will last almost indefinitely. There is other media you can use as well.
 
If you click on the link in my sig, it will bring you to a wealth of information for beginners. Good luck, and I hope you can save the rest of the fish.