Sounds like your system should support sps and grow it...
- its possible your sps react to the large water changes with little growth (meaning they adjust to their current parms for a few weeks, then the parms change with the new water) Surely, after a few weeks, your levels fluctuate, it might not be enough to damage them, but could be stunting their growth. Have you checked your parms just before a water change and then after to see how much of a dif there is?
- If the whites in your lights have a high kelvin temp (14k +) depending on your sps, it may require a lower colour temp for growth (6K - 10K)
- Depending on your particular LED's (i dont know the specral output of yours), your sps may be missing a portion of wavelength that your led's are not providing, reseach has shown this to be all too common with LED's, I know I dealt with this issue with my lights also, this is why the newer lights have greens, reds, violets ect.. added to them. Google the led studies done by Sanjay Joshi on advanced aquarist (sorry no link) there are several of them.
- I have not used the amino acids you are using, you could try a different brand?? IMO, it's one those things we buy to aid our corals, but realistically, we have no idea what consentration is actually in the bottle, it could be water for all I know
Anyway, these are just some thoughts, a lot of sps grow soo slow for some, and take off for others....
ps. send me a PM if you are interested in viewing each others systems, since we are so close by, dont know of many hobbyist in Lander...