some trouble in the garden

I picked up 4 clones from my dispensary a couple months ago.
I have them all in flower now, but my romulan is having problems. I have 2 other plants in the rdwc setup that are doing great, on the same nutes. We are in week 4, and the romulan has fan leaves with what looks like mag. def, the lower bud leaves are curling down, and have for a while. the top bud leaves are curling up and praying.
Running dynagrow grow/bloom, and calmag at 3ml per gal.
750 ppm
ph drops to 5.5 daily, I correct it to 6.0
I had some algea buildup in the white tubing I used, but replaced now with black tubes.
Res temp was at about 70.
Running 1ml per gal gold zone root conditioner
I have an indica, and a stativa growing next to the romulan, and they look great.

Any suggestions for me?

you may want to check your water and make sure that you dont have a chloramine problem,some places are useing it in place of chlorine because its cheaper but it is very hard to get out of the water,you can use drops for fish tanks that say on the bottle removes chloramine or use rain water if you have a way to collect it,I switched to rain water and melted snow and my plants have never looked better. good luck also make sure that you killed that algea or you will have never ending problems

I did a little flush today with clearex, and refilled the res at 580ppm.
My guess is that she just cant handle the nutes, combined with strong lights and dry air.
I hope that backing off a little more will help.

Hope it helps. Looks like she got some nice buds on her.