Hey Happy your plants are looking great and what a set up you have. id like to chime in and this post might be a bit premature as im only about halfway through your thread right now.
First of all i would not follow tangs feed schedule as you are growing photo periods and as we all know autos dont like to be fed a lot but photos on average do ( tangs schedule is for autos not photos). Your getting a yellowing due to the plants utilizing the nutes a lot faster under the hps compared to MH lights so i recommend you bump up the feeding to at least 2-3ml per litre and see how they respond.
Secondly you more than likely wont need cal/mg as only autos are very heavy on it and photos only need a little touch of it in the res near the end of flowering if at all. Cal/mg will More than likely cause lockout and problems by adding cal/mg when there is no deficiencies so dont use it unless you so a mg or cal def.
In my opinion ph should always be between 6.4-.6.6 when using a soil or soiless growing medium. Sorry for butting in dude i really just wanted to try and help you out as i read what your doing. hope i helped dude and best of luck with this im subbed.
Hey Grim
Yip you're totally right about everything you're saying here. Well at least I believe you are!
TaNgs schedule is for autos not photos and photos will probably need more nutes than TaNgs schedule specifies.
The pH should be lower definitely but for Plagron LightMix i was advised 6.0 - 6.5 direct from Plagron so I'm going to shoot for 6.2 - 6.3 pH
The yellowing of the plant is probably because HPS makes the plants untilise nutrients (or at least certain nutrients) faster than MH. Which is probably tied into my pH being too high and my nutes being too low.
The extra Cal/Mag again you're definitely right, probably unneccessary and adding too much when it's not needed can cause lockouts and next grow I've decided I'll be ditching it. Ofc I'll keep it on hand just in case. The main issue is that I use RO water which has all the natural cal/mag stripped out of it. However I wrote to Advanced Nutrients and they said as long as I'm feeding enough Sensi A&B I should not need it. However if I do add it, only add 0.2 - 0.3 EC worth at the most.
Dont' be sorry for butting in dude I highly appreciate it. You've basically said all the things I've been thinking and it's good to hear someone confirm all your suspicions and your plans. Makes moving forward more confident.
So next grow is about to start, I've the seedlings germinated and I'll have one half of the room fed by one tank and the other half by another tank. So will get to play with the feeding schedule (two feeding schedules going per grow) so exciting times ahead. Hopefully I can come up with a really good 'Autopot PhotoPeriod' grow schedule to share with the AFN family.
Later Grim, much respect.