Corys Are Dying! Help!

[animalhouse512]

Hello all. Need some quick help here. I have a 70gallon tank with a bunch of live plants, 75gallon HOB filter, and these fish:  3 panda corys, 4 albino corys (1 about 2 years old, the others bought and introduced approx 3 days ago), 5 peppered corys ( 1- 3year old, 4 new additions added 3 days ago), 10 platies, 1 farrowella, and 1 bristle nose pleco. I had originally 5 of each type of cory, but they keep dying. I have had this tank established for over 4 years. We did a 30% water change 4 days ago and rinsed off the excess algae from the filter housing and media bags. I noticed a nitrite spike about 3 days ago...after adding more corys (probably what started the ball rolling) so I did another 10% water change and added prime, just in case. Today after another lil fella cory died, I tested the water using the API dropper kit. Results: Ammonia .25ppm, Nitrate 40ppm, Ph 7.4ppm, and Nitrite 0ppm.I just added a bit more prime to try to combat the ammonia in there, but what else could I do to help?What is going on here? Why are my lil fish bros kicking the bucket? I got all the ones that have passed from the same fish shop...Im just really puzzled. Is my tank over stocked or did I screw up by cleaning the filter, or maybe bad supplier from the fish store? what is the deal?!? HHHEELLPP!
 
 
SAVE THE LIL FISH BROS!

 

[Munroco]

Tank certainly isn't overstocked. If I read this correctly you added 7 cories? Are the ones that died all from these 7? Is definitely possible that there was a problem with them before you bought them if this was the case. Rinsing the media bags wouldn't have much effect . Do any of the other fish seem in distress?

 

[animalhouse512]

So, yes.. all the ones that have died have been from the same place. I added 4 of the panda corys about 2 weeks ago and the other albino/peppered 3 days ago. One albino immediatly seemed distressed and died with in 4 hours of being in the tank. The other 3 new albino corys are now acting distressed. Staying vertical near the filter or swimming only in one spot at the top of the tank. The old albino and  peppered cory are fine. Happy as ever with new buddies.

 

[Munroco]

I can only think its the change of water thats affecting them, unless they were in a bad way in the LFS and I'm sure you would have noticed. I don't know if you can find out what their water properties are, in particular PH level?

 

[animalhouse512]

I can only think its the change of water thats affecting them, unless they were in a bad way in the LFS and I'm sure you would have noticed. I don't know if you can find out what their water properties are, in particular PH level?

 Called the LFS. They keep their Ph at 7.0, so maybe that would do it. Thanks for your help. Keep your fingers and toes crossed that these other little dudes pull through.

 

[Munroco]

I hope they do, somehow it seems worse when its cories. You could always put a bag of peat in your filter. I don't know how quickly that would work. If you could get it slightly lower then take it out and let it rise again it would be like acclimatising them gradually.

 

[Crystal90]

Just curious, you didn't mention how you acclimated the new fish. Did you quarantine them at all? I'm not criticizing (I did a stupid thing just 2 weeks ago and lost a tetra and a gourami)  

 

[Ridasha]

Good day to you.  How are you making out?
 
There was no mention of temperature I think.  Cories and plants like it warm.  My cories and plants love 80-81 degrees as does beneficial bacteria as opposed to when I had them at 76.  You mentioned live plants but also a nitrate level of 40 ppm.  Does not sound like your plants are doing well and if not will contribute to poor parameters.  It is only my opinion that nitrates should not be any higher for freshwater than it is for saltwater, particularly for cories.  Healthy plants will take care of the fish for you.  With planted tanks the focus shifts more to caring for the plants than fish. 
 
The four planted tanks I own use surface agitation and warm water (81)  for CO2. Iron, potassium and micros (as needed), and 6500K daylight cfls. All tanks are 0, 0, and trace for nitrogen parameters.
 
Also you mentioned you used prime as part of the 30 percent change and mentioned a number of 0.25ppm of ammonia.  If that test was done after the prime it should be mentioned that if your water does have chloramines (Chlorine + Ammonia) Prime will release a non toxic Ammonia that will be read on test.
 
Finally my opinion is that your filter is fine but your nitrates are way too high for cories and likely due to plants not doing well.  Good luck, I wish you well. If it were me I would do a 90-95 percent water change with double dose of prime before adding.  Doing this in the morning with a full 12 to 14 hours of 6500K light on the tank afterwards.  Use healthy floating plants in an emergency.
 
Regards,  Dave

 

[DoubleDutch]

Traces of ammonia and nitrites in a established tank is very strange and probably culprit for your losses. Sounds like you had a crash.
These three Coryspecies are all coolwater-Corys so the suggestion to raise the temp, isn't a good idea. They also will cope perfectly with a Ph 7,4. Don't mess with that !! A stabil one is much better than .4 lower.