They were 40+ and now usually between 5-10.
Similar symptoms as iron deficiency?
Ps. Thanks for the help all
So let's assume your nitrates are 5-10ppm. Adding 50% of an EI dose (3.75ppm 3 times a week) will raise your nitrates to no more than 33ppm which is well below any dangerous levels. You really only need around 10% of EI.
I hate trying to reduce dosing to not "waste fertilizers" though. That's why I say dose 1/3 of full EI for Excel based tanks. Then there is NO question it's not a nutrient issue. Logic dictates that we can eliminate deficiencies by dosing "above the barrel". Trying to narrow down nutrients to limiting levels is like playing Russian roulette. You WILL eventually lose.
The other option is to dose "above the barrel". The excess is not harmful and we know for a fact the plants are getting what they need. No need to wonder if the test is accurate or if the dose is enough etc. Just dose more than enough. That's the idea behind EI.
Modifying a method that works is asking for trouble. Trouble we see all to often. People rely on tests or think their tank produces enough X, Y or Z. It's all subject to error. Supplying nutrients is simple. Dosing more than we need is not harmful. I'm not sure why so many people choose to ignore this.
Again, I'm not trying to berate you. I'm just trying to explain that there is no need to wonder whether nutrient A, B or C is causing problems.
I'm usually not a big supporter of identifying deficiencies for the reasons above. Iron and nitrogen deficiencies can cause chlorosis. Usually iron will be on new growth and nitrogen is on old and new. Instead of relying on this approach just dose above those limitations.