My CO2 diffusion is much less efficient than yours -- just a Do!Aqua glass diffuser underneath a 240gph Koralia Nano powerhead. With my Milwaukee SMS122 pH controller, my pH is maintained at 6.1 for the entire photoperiod. If I put some tank water in a container and let sit for 48 hours, my "actual" pH is 7.7-7.8.
Now, my tank is a very high light experiment, running 4x54W of the strongest T5HO lighting (ATI Powermodule - made for reef tanks), the lights at 12" from the water surface. With this much light, I have to pump soooo much CO2 and sooooo much dosing every other day. Check it out:
1 tbsp GH booster [12ppm potassium, 5 ppm calcium, 0.89 ppm magnesium]
1 tsp of KN03 [15ppm of nitrates, 9.6ppm potassium]
1 tsp of KH2P04 [19ppm of phosphates, 7.82 ppm potassium]
(potassium totals to 29.42ppm)
CO2 is at approximately 47.7ppm. I know the KH/pH/CO2 calculator is not 100% accurate, but it's a pretty good estimate, considering my 1.6 drop in pH.
No problems with solubility here --
CO2 - 47.7ppm
K - 29.42ppm
N - 15ppm
P - 19ppm
Perhaps your dosing levels are even higher than mine?
Tank is 120cm x 45cm x 45cm. 4 yr old Aqua Soil, a few pieces of driftwood, and tap water treated with Prime. pH is 7.7-7.8, but goes down to 6.1 during photoperiod. KH 2, GH 6.
Oh, with the API Nitrate test kit, the water crimson red for me.....so over 80ppm? I really need to make reference solutions to get a more accurate reading of my nitrates, before my dosing. I do know that less than what I'm dosing right now leads to diatoms, which goes away after I bring my nitrate dosing back up.