Strange discus behaviour

[axl]

Hi Guys,
its been a while since i have posted on here, so here i go. I have got a 6x2x2 planted discus tank with the following specs

6x2x2 tank
co2 incjected with ph controller
ph 5.9 by the end of the night
ammonia - 0
nitrite - 0
nitrate - roughly around 5 to 10ppm for plants
wc every 2 to 3 weeks of 30% ( have been told by a discus expert that discus don't like to many changes to there water and im only using straight tap water.
2x 300w eheim heaters
1 x eheim 2217
1 x eheim 2280 pro 3
1 x uv sterilizer
lights: 2 x 1500 led lights with only 3 rows going at the moment

This setup is only 5 months old and currently has got 6 discus in there and roughly 100 cardinal tetras, with various catfish. My issues are that the discus are always hiding and come out every now and then, they have good color and eat mainly dried aussie worms from mal. 1 of the spotted reds has always got his stress bars showing and i don't know if it is because of the co2?. All the cardinal have great color and swimming around good and the discus just hide behind the driftwood with them coming out every so often. Whats the go??

I had trouble with hole in the head due to buying 2 turqs with this at the start but are now over this.
I ran out of co2 the other month and they were eating a lot better it think and swimming around heaps when this wasnt going, could this be the case that co2 is causing this. I would love some help on this issue.
Cheers Axl

[BobbyBruce]

Hi Axl,

My guess would be that the CO2 injection means that your discus are low on oxygen. When I first had a school of discus in a heavily planted tank they would be gasping for air in the mornings as the plants utilise O2 and produce CO2 during hours of dark.

The discus were much happier in the mornings after I introduced airstones overnight to ensure higher levels of O2.

Just out of curiosity I seem to recall that your tap water is low to mid 7 ph. Going down to 5.9 or thereabouts is a significant fluctuation in pH.

Regards,

Bob

[axl]

There not lacking oxygen because the solenoid is hooked into the light timer so it goes off at nights, plus there is no sign of them breathing heavily during the day , both filters are creating surface agitation, in the morning the fish don't have there stress bars showing. There is minimal ph change when the co2 is off the ph is 6.3 and when co2 is going its 5.9 by the end of the day. Ph doesn't swing to much when doing water changes because I'm only doing 30% at a time so it dosent go up much