Typically i don’t adjust wattage’s and just leave it at my full set value all the time, only time i turn it down is when its completely empty with just seedlings starting out as if i don’t heat builds up due to all the light bouncing around having nowhere to go, but once you have a plant or two of alright size then its back to full.
As for the pH yeah more dolomite lime could possibly fix the issue even if ive already tried 4+ tbsp a gal of mix, but its an issue that shouldn’t be there in the first place so no sense chasing my tail and just avoid the situation to begin with, that being avoid the more generic Promix potting mix and only go after the HP or similar bit higher end mixes, or just go back to coco which will likely happen eventually.