Any advice please folks

A week ago I noticed what looked like potassium deficiency on a couple of these top leaves, going from images on other sites...so thinking there may be salt build up causing this I done a half flush to hopefully help that out. Then I got it into my head that it was a bit of light burn so moved lights even further away. Also noticed some blackish colouring on some of the small leaves around the top bud...so that got me back thinking it is potassium deficiency....But it seems now like the plant isn't taking up water as quickly as before the half flush....the leaves are starting to go that limey colour but I'm hoping that this is because it's near the end of the cycle? Any advice about the water intake....is it just because it got drenched and is taking a while longer to suck that up? I'm paranoid about watering/feeding it now incase I give it too much water...but if I'm waiting for the top inch or two to dry out...that could be a long time. Just gave it about another half litre with nutes on top of damp soil. About 2 weeks flowering left I think but hopefully some of you guys with more knowledge can tell me if this looks correct..or is it due cut sooner than that....I'm going to be checking trichs later. If there is a couple of weeks left and it is potassium deficiency what I can do? I have a PH meter coming today ...before I was using the paper strips.
 

Attachments

ph level at 4" deep is 5.0 , but 6.0 at an inch or two, just gave it a 4 litre baking soda flush, as i've read this can raise the ph level...am i too late?.... hope i'm not hurting my plant whilst thinking i'm helping it...HELPPP arghh
 
Top