Can't get nitrates under control - need drastic action

[Allistah]

When I got home the pleco was dead. He had huge white areas on him about the size of a quarter on his head. All the others look to be going ok though. The catfish is still alive as well.

The tank temp is at 83 currently and the target is 86. This Fluval E200 is nice because it raises it slowly. My girlfriend added the salt solution to the tank today while I was at work.

I took readings today as well when I got home:

• Ph - 7.8
• Ammonia - 0.0
• Nitrite - 0.25
• Nitrate - 10

It was interesting that the Ph dropped from 8.0 to 7.8. Maybe the salt did that. The fish look like they're doing a bit better but still having issues.

[meegosh]

Did you drop your water level to get more aeration? At the higher temps this is critical. Sorry to hear about your pleco. I haven't heard of salt altering pH before. When is the last time you did a water change? If it has been a while the excess organics in the tank will create acidic compounds, lowering your pH.

[Allistah]

On Sunday a complete water change was done and all the gravel was washed so the tank was 100% clear and clean with new water. The water going in the tank has a Ph of 8.0.

Ok, I also lowered the water level a bit and the HOB filter is now giving more air to the tank. Lots of tiny little bubbles moving around. Even without the air from the filter, I have two long airstones that span about 75% of length of the tank in the back (55 gallon long tank) so they should have plenty of air.

The temp target is still set at 86F. The temp is moving up slowly and is currently at 84.5F The Fluval E200 heater is doing a good job of moving the temp up slowly still.

All the fish are fine this morning so things are looking good so far.. Except for the pleco yesterday.