winsbxnyc, if you don't already have a TDS meter I would suggest that you get one. It will save you $$ in the long run. You will be able to test your ro/di water to see if you do need to change out your membrane.

If you get 0 reading you'll know that you don't have to run out, and replace membrane or di resin saving you some cash.
I use
Salifert for everything but ammonia, trites & trates. For those I use the API.
Causes for hair algae can be many. For instance I just had a small outbreak in my 155 gal. that was due to the death of my fish. I recently lost 6 fish from 3" to 7"or 8". I was able to pull the 2 largest, and one of the smaller ones. Leaving 3 medium size fish in the tank. Within 2 days I had a di
atom bloom & some gha. I did test my ro/di just to be sure, and the reading was 0. I didn't test for P04 or trates since I was/am pretty sure it is an ammonia spike from the dead fish, and the Nitrifying Bacteria death.
I stopped feeding the lonely little blennie left, did a 20% water change, added fresh carbon, and reduced the photo period from 12 hours to 4 (I run LEDs). Next day diatoms & GHA are nearly non existent.
BTW, when I ran MH with PC I only ran the PC for like 12 hours, but the MH I ran only for 5 hours.
With you moving your old sand over you may have cause a small cycle, add to that you are running the MH a bit to long in my opinion.