Brown spots & yellowing of leaves moving upwards

Hello

First of all let me say how useful this site has been. I dunno what I woulda done without it. I got a pretty good yield from my first grow much of which was due to advice i found here.

I'm into week 3 of veg, with 3 plants on the go, growing under a 250w HPS, the strain is Orange Bud, I'm using Vitalink nutes with NPK 10/5/16, I'm growing in normal pots with cellmax/(1cm squares of rockwool), I also top up my nutes with Vita link liquid silicon. I take a ph reading before watering which is usually around 6.2. I water whenever the pots feel light.

I am following the feeding programme provided to me when i purchased the nutes but have noticed some yellowing at the bottom of the plants which is moving upwards and now all 3 of my plants are developing brown spots on the leaves and going crispy in some places. Also I've noticed a big build up of algae on the surface of the rockool.

On my last grow I had one female and 3 weeks into flowering encountered a similar problem, resulting in pretty much most of the fan leaves dropping off the plant. The buds were fine though i Yielded about 2 Oz. Not bad for a first attempt i thought. This time round though the problem has kicked in earlier and so i desperately need help as I'm worried this will affect my Christmas crop.

Can anyone please help me?

If you are growing in rockwool....your ph should be between 5.6-6.0. I have a feeling your ph is too much on the edge and you are locking out nutes. Drop it to the above number if the media you are growing in is not soil.

Thanks for your advice Weedhound. What should i do next? Flush through with an appropriate strength solution?

That is probably a good idea.....flush with ph correct water and check the ph of the runoff coming out the bottom.....make sure they are the same (if not...flush until they are).

Good luck.

Ok I flushed through with Ph correct water and checked the run off and the PH was the same. I'll monitor them over the next few days and let you know if there is any difference.
Thanks again for your help

You're welcome....next time you water them. give them 1/4 strength dose of nutes in ph correct water and see what they do with it. If they act happy (and I think they will) you can work the nutes up slowly from there.

PS....SLOWLY is your key here....its ALOT harder to fix nute burn in a plant then a deficiency.

Ok
I'm due to switch to flowering within the next few days, and obviously change to bloom nutes, should i hold of the switch until i know they're ok?

Yes....I'd give them at least one more grow feeding and more if you have the time.....low strength.....before turning them.

Ok thanks for all your help. I hope you're right
I'll use a few drops of superthrive as well and see if that helps any. Just so i understand what i did wrong i need to ask a few more questions.
Ok so i was feeding them with a ph that was too high, meaning that the plant was unable to absorb the nutrients, is that right?
What exactly causes the nute burn?
With the feeding schedule i was provided with my nutes, i use 1/4 strength for weeks 1&2 and 1/2 strength for weeks 2&3, but often by week 3 they require watering twice in a week, should i then give them 1/2 strength solution twice in a week? Or is it better to give them the nutes at the beginning of the week and if they get thirsty top up with water?
Hope that makes sense