Am I dealing with an ULN issue?

[Myka]

Sometimes, guessing what the problem is in your leads everyone down the wrong path. I'm not convinced it's an ULN issue because you're still getting some color on the NO3 and PO4 tests. Maybe double check that. Maybe you're not getting accurate tests, and maybe NO3 and PO4 are both undetectable. If you stop using GFO, what does PO4 get to? What was PO4 at before you added the GFO?

FYI, provided the KH reading of 7.6 dKH is accurate, that is not high enough to cause burned tips from ULN in my experience. I've mainly seen KH of about 8.5 dKH and higher cause that problem.

So...how big is the tank and what do you have for fish? How often do you feed them?

Are you sure there are no pests in the tank? Which dips are you using? Are there ANY Acros that are doing well? If so, which species are they?

What do you have for lights? How many hours at what intensity? Have you used a PAR meter?