yellowing leaves??

First time garden here...ok, our girl(I know, only one) is looking pretty good in the bud depot....but now we are seeing yellow creeping from the bottom leaves and slowly working it's way up and some leaves are dying. our girl is pineapple chunk, in a three gal. pot. 70% foxfarm soil 15% worm castings and 15% perilite with lighting of 1-400hps from top and 1-20watt cf pointed at the bottom of the girl 1 fan for circulation. She was in veg state for 5 weeks and currently in the 5th week of flower. We watered every 2-3 days with ro/di water with microblast and grow nutes at around 7.0ph with around 6.0ph runoff while vegging with no problems, then ro/di microblast, grow and bloom nutes every 2-3 days until the yellowing got more severe then we stopped the nutes flushing a few times now only using water but noticed the runoff ph now lower around 5.0(measuring with the drops in water compare to chart). So I know I need to raise the ph but what other problems may be happening?

I've been hearing about calcium def, how is calcium added? I have some calcium carbonate that I use for my saltwater fish tank, can that be dissolved in water and added? What is lime used for?

Forgot to mention, we did have gnats pretty bad 3-4 weeks and had a hard time evicting them. Finally decided to smother with a top layer of sand That is also when the runoff soil ph started turning out to 5.0.

To make an proper verified diagnosis we'd need pictures.

As to the my thoughts if you're 5 weeks into budding the plant starts using alot of it's energy from it's leaves (Generally starting at the bottom) and puttin them into it's buds.
You should be getting pretty close to harvest yes?
But i wouldn't go of any defiencys without proper photos..

As for the lime it works as an alkaline and brings the pH up.

Geez sounds like u overfertilized flushed and ph is still outa whack. Check soil ph, when correcting use water n ph whatever I usually have rising ph in soil. So it was around 7.5 due to friend watering. So I used ph 4.5 water flushed to soil ph of 6.8 and will slowly correct every watering. But I would wait til dry to water again. It will prob need nutes too so I add a little guano on top and water in.

They have some good organic teas in the organics section. Check them out.

ur plant is leach nitrogen from its bottom leafs and it will continue all the way up the plant unless u fix it always ph ur water b4 watering always! i would foiler feed a lite does of some grow food and continue to feed

sorry for the bad pictures, i hope they help...

That looks like pretty natural yellowing of the leaves. The plant is dying and doing everything it can right now to create big sticky buds to catch male pollen. One way it does this is by pulling all of the stored nutrients from the fan leaves. You are dialed in right now, enjoy.

From my experience it seems pretty normal. I think under normal lifecycle conditions, this is part of the fall dying phase of the plant. I say normal because some plants just don't want to follow the rules and want to become perrineals. A lot of people seem to want to fight this condition but I don't think you can. At this phase the plant is just pulling the last bit of go juice from the leaves and it's done.

Thanks for the help soo far...i do have a question on ph though, is there a formula for adjusting the ph of water your about use when the runoff of the previous watering was 5.0.

So for instance my last wateting...ro/di water is 7.0 and runoff was 5.0, so if i take my 7.0 water use a ph raiser and make it 8.5 will that in theory make runoff come out 6.5 or is it just a trial and error thing. Thanks again from a newbie