when u mean be careful of co2 hightech, u mean co2 overdose and PH swings?
cuz i have a ph controller and it keeps PH day and night at 6.8-6.9 all the time.
anything else i need to be careful of in hightech plant tank with discus?
what about dosing fertilizers NPK, micro?
are 4" size considered adult enough?
Yes, that's basically what I mean. And it's good that you have a controller for maintenance of pH stability.
BTW, you don't run your CO2 at night do you (24/7) ?
If you're well experienced with running a high tech pressurized CO2 system, then there's nothing specific I can think of that should/could present any serious problems for the discus, including dosing NPK and trace elements.
4" discus are near adults, but will not likely have as well developed immune systems as 6" adults, the latter which also need lesser feedings than 4" fish - hence easier to maintain good tank cleanliness.
In this type of environment, further growth of 4" fish may tend to be very limited (i.e. some stunting risk), but if that doean't bother you, then go ahead with the smaller fish.
If it were me, I would still hesitate to take on this kind of challenge with discus, as I would not wish to be faced with the potential hassle of having to correct/change/alter/backtrack/watch & maintain all systems properly.
I feel it would take more time monitoring this type of set-up than the time it takes to do more regular wcs, and maintain a low-tech enviro.
And regardless of the video host's experience & results with this kind of set-up ( he's able to monitor it well daily in his shop), I nonetheless can't felp feeling the discus may not remain as healthy & disease-resistant over the long term, as those receiving regular large doses of fresh, clean water.
But hey, that's just me - to each his own.