I'm using the nicrew deluxe light. Pretty sure we've had a conversation about it before, there was someone on this forum that par tested the light and showed it was actually considered quite high. I'm still not certain about it, but it seems extremely bright to me at 100 intensity. I know that is not necessarily indicative of par though.
Yes, I vaguely remember this and the high light with good quality aspect. Getting at your interest for higher growth is, of course, a little difficult because it is hard to know how close you actually are to maximum potential growth, given your particular setup.
Your light seems to be right. The next thing I would focus upon is CO2 and, as you probably know, DIY CO2 can be very tricky as compared to pressurized delivery. If you haven’t already been challenged on how you are measuring CO2, maybe this is a good time to do it. So, how do you measure CO2 levels and is it consistent throughout the photoperiod? Also, do you have good circulation with all plants very gently moving from top to bottom? The filter problem may be impacting things. You generally don’t need a lot of media to do the job, e.g.; I use no biomedia or chemical media in my filter - only some filter floss to capture particulates. I’m not suggesting that you do this, but biomedia in filters is usually very efficient.
Your nitrate sources explain why the Purigen does not seem to be working, so you may be able to remove the Purigen. Purigen does not remove nitrate. It removes the organics that turn into nitrates. So, it has no effect upon the NO3 from your tap water or the dosing.
The nitrate from my water is about 20ppm. I add about 18ppm of nitrate per week through the all in one fertilizer. Typically I see the nitrate above 50ppm by the end of the week. I just expected the heavy plant load to consume a substantial amount of nitrate.
I think you have the answer to your question about why your nitrate is so high. You can use the various nutrient accumulation calculators (Zorfox’s calculator is better than RotalaButterfly for nutrient accumulation) to see why. I’d stop dosing nitrate and see where it takes you. NO3 uptake, at most (unlikely in your case), should be about 3ppm daily, but this is usually reduced if ammonium is plentiful, albeit unmeasurable.
After verifying CO2 levels and reducing nitrate, then I’d start to approach fert balances, but give it a few weeks after you get your nitrate under control before doing that.