Dying Cardinals

[Brian422]

We have been keeping fish for a number of years with very little problems. We started up a new tank, (approx 200l) for Cardinals and Discus. A week later we introduced plants. We had the water tested after 2 weeks and it was fine so started to stock with Cardinals. Over the last 3 weeks, the Cardinals have been dying of at a rate of almost 1 per day. The pH is 8.5 - 9, KH is 5, NH4 is 0.1, NO2 is 0, NO3 is 10mg/l. The fish do not appear stressed, there are no external signs of disease. Can anyone tell me why we have such a high mortality rate?

Thanks in advance

Brian

 

[the_lock_man]

You're showing a small level of ammonia - I wonder what the maximum level of that was in the last 3 weeks? Could that be the issue?

 

[Brian422]

It could be. The NH4 was 0.8 at its highest. We did a 30% water change add bacteria. We had rapid plant growth and lots of algae growth but the plants have settled down and the algae growth is now under control. I don't know whether plant growth and algae growth can cause problems.

 

[the_lock_man]

I don't think that plants or algae are the problem.
 
If you had ammonia at 0.8, and did a 30% change, you only brought that down to 0.5ppm, which is still pretty toxic. It could well be the problem. Additionally, your pH is very high, and at high pH, very little ammonia is in the non-toxic NH4+ (ammonium) form. Your test kit can't tell the difference between NH3 and NH4+, the latter being non-toxic.
 
I would suggest testing daily (I assume you've got your own test kits, if you've been keeping tanks for years), and any time you see ammonia (or indeed nitrite) up to 0.5ppm, change 50% of the water - if you see a level of 0.5ppm, then change 90%. Hopefully, that will stop the deaths.

 

[Brian422]

Thanks. I'll change the water and try to lower the pH.

 

[the_lock_man]

Don't try and muck about with pH, it's often more of a problem doing that than leaving it alone. Especially if you try to use chemicals to do it, it's often been the case that the effectiveness of the chemical wears off, and the pH bounces back to where it wants to be, causing the entire stocking to die. I believe Discus are quite intolerant of water issues, so best leave pH well alone.