I check it this morning and it was reading 6.2 but I just changed the water on Friday and pH'ed it at 5.8 should I drain my res again pH it to 5.8 again or should i go lower?
6.2 is NOT a high pH.
5.2 to 6.2 is the range for hydro
5.8 is perfect
anything lower than 5.2 or higher than 6.2 needs amending.
And, if it does need changing, there's no need to drain the res.
Simply add pH down or pH up.
Dilute a little in at least 1 litre of water
add to res when the plants are not being fed (when pump is off)
and make sure to mix it well into the rest of the water.
Add 0.2ml with 1 litre water -mix it up -leave for 10 mins
TEST pH.
See how much the pH has changed.....
Pretty soon you'll knowhow much pH Down (or pH Up) will change your pH level.
It's simply not feasible to drain your res every time the pH goes out of range.
And don't get too uptight about it.
5.2 - 6.2.
If it's 6.1 or 6.2
don't try to make it 5.8.
5.2-6.2 is the Sweet Spot
Soil grows need a slightly higher pH
7.0 is the best.
An EC or PPM reader will help you to know exactly what you're feeding.
Overfeeding is much more serious than underfeeding.
And as you've already overfed them enough to cause nute burn before (which will have stunted them)
I wouldn't risk it again.
Better to leave them a little hungry - before you can more accurately test their nute levels,
than to give them too high a concentration of nutes - and potentially cause much worse problems.
I can back up every suggestion I make with supporting evidence from published experts (checkable sources).