Its the phosphorus being used changing the ph i think mate. Try giving the ph at 6.2 and see how that changes things 

@macky     when advanced nutrients claims ph perfect and then I swings hard like that I always think I must have ratios wrong 

So by striving to achieve a static res I should completely ignore the instructions on the advanced nutes labels   0.7 Ec seems to be that number right now  that's like 30 mls  each A and B and 20 mls cal mag in a 50 litre res   leaving very little room in the Ec for big bud     Am I doing this right?   We use RO water 60 ppm

yer advanced say like 4ml per litre right? i never went over 1.5ml per litre with it, but the EC i ran on was always pretty high, 1.8 during flower with big bud. The pH perfect stuff is ok, but needs to be used at full dose to really work, and at them levels it over feeding the plant

@macky  yes 4ml per litre they recommend    I am running less than 1ml/ lt  and Ec is static  so that's like 25% of their minimum recommended  rate    the rate they suggest for seedlings   so  I mix in big bud and cal mag at 25% of their minimum recommended rate hoping I am keeping the ratios right ?

Depend son the stage of growth mate, put a pic up for me

They are 5th week of flower and 4 ft tall   in dark right now   I posted photo few days ago trying to identify mag deficiency

So, you're using Sensi Bloom a n b, with big bud now right?

I would be using about 1.5ml of a n b, and 2ml at least of the big bud per litre, Ec will be around 1.4

@macky   conniseur and big bud powder   I feel like I'm underfeeding when I mix but the Ec stays static so I thought it must be right

dont use the cannasuier any more, it wont be necessary, just the A n B and Big Bud. in a couple of weeks, when trichomes are about 50% milky 50% clear, we switch to over drive, and get rid of the big bud.

Trust me, the labels are guides lines. This way is tried and tested 😉 

Gradually raise the feed over the next couple of days. if you go too fats you might get nuit burn, but a gradual rise will see the plant adjust with it. 

@macky he’s not using Sensi coco, he’s using “Advanced Nutrients pH Perfect^® Connoisseur A & B” The higher end stuff

@macky   I will definitely try it thank you   I just gotta ask tho how is my res static at .7 Ec when it should be 1.4 ?   

@monkeydothats right thanks

I've thought for awhile I was underfeeding  small buds and slow but my res stays static suggesting Ec is correct