Par is 90-110 at substrate level. Measured with a Seneye reef par meter. Seems accurate enough from what I have seen in reviews.
I don't add any extra K. The potassium is indeed only from dosing N and P. So I should start dosing 5-7 ppm extra coming from KSO4?
I will up the PO4 and Mg.
I have a bottle of Seachem Flourish Iron. I read this is ferrousgluconate and isn't affected that much by pH. It only needs to be added daily. I can do that, but how much should I add? I realize this can get expensive fast, but since I have quite a small aquarium I am willing to go this route. Ferrousgluconate in powder form isn't easy to come by here in the Netherlands.
As for my high KH, I can buy a RO/DI filter and use half tap half RO/DI water. Don't know if this will make a big enough difference, since there is quite some extra work involved.
I was also wondering about the amount of CO2 I have to add for a pH drop of 1.3. I add around 4 bps, seems quite a lot for a 60 liter aquarium. Maybe this has something to do with the high KH. I have a CO2 regulator and inline diffuser from CO2Art. Output is a spraybar on the back of the tank. It is pointed down quite a bit, flow is bouncing of the front glass going down, over the substrate to the back and then comes back up.
I have been struggeling with adding CO2 for a long time. Never seemed to be enough. Was a victim of the dropchecker is green tunnelvision for a long time. Until recently the new growth isn't getting affected by BBA. The pH drop of 1.3 is probably doing the trick. Fish seem to be fine, although I have never pushed it that high for them to start showing signs of distress. I measure pH with a Hanna Checker plus, which I calibrate with 4.01 and 7.01 buffer at least a few times a month.
Also greatly reducing light intensity has made a big difference. I kept reducing intensity and duration, but nothing seemed to help. I was running the lights at around 70 percent intensity and only a total of 5 hours a day, when I first measured the par output. It turned out I was still blasting the substrate with 250 par.
I know you guys always say when people are having algae issues, reduce lights and up the CO2. I just never figured out I had to reduce it by that much. I think I run the lights at around 30 percent intensity for 5 hours plus some ramp up ramp down. For evening viewing time I use only the RGB leds, a bit heavy on the red side, at such a low intensity it gives a par reading of 0. Amazing how the colors, although not that great yet, can pop.
At full intensity the lightbar reads 350 par at substrate. Crazy how overpowered some led units are.
Anyway, I will post a few pictures in a few weeks when plant health is hopefully improving.
Thanks for all the feedback and suggestions!