Verifying I don't need to add fertilizer...
I'm an experienced fish guy (and experienced lab guy), but very new to the planted tank side of things (only about a year). I've had a number of failures where few poor unfortunate plants didn't make it, but things are going generally better now. I've got a fairly lightly planted tank (2 swords; 1 ea. crypt wendtii, parva,willisii; and a largish (30x10cm) carpet of Christmas moss), with a fairly high load of fish (~30 small tetras and a half dozen tiny peppered corys) in a 56g tank. I run what I believe is medium light (two Coralife Aqualight S LED, right at top in 24" deep tank), inject CO2 and best estimate based on kH and pH CO2 controller is I'm at around 20ppm.
I have been using the API test kit for Nitrate and Phosphates, and recently got the Seachem kits for the same to get a bit more precision.
My question -- with both kits, it is clear my numbers are pretty consistent -- 15-20 mg/L Nitrate (I believe both test NO3-), and 1.75 mg/L (1-2 on the less precise API kit) of Phosphate (again, I believe both test PO43-)
My understanding is that the goals with EI are for Nitrogen, 5-30 if using Nitrate testing, and for Phosphorus 1-2 if using Phosphate testing.
So is my bio load simply high enough that I am getting sufficient levels of both (for now) for my plants? I am currently adding the recommended bottle levels of Flourish Potassium (since I can't measure, and I'm certainly not getting it from other added ferts, since I haven't been adding) and Flourish for trace minerals.
I keep having a nagging feeling I'm reading it wrong (particularly around converting phosphate to phosphorus and nitrate to nitrogen levels) and really should be adding some Nitrogen or Phosphorus...
Plants are growing slowly (slow growers), but I have some BBA on some leaves, so as part of my "getting things right", I'm trying to verify that I am reading the dosing instructions right.
Thanks in advance for any feedback on "I'm reading it wrong" or "Sounds right"!