Well plants do different processes during lights out and day light. They release starches etc and hydrogen ions during lights out so while this may not be huge it can add up with other effects. Like high CO2 levels produced during plant respiration over night. Now air pumps increase gas exchange and so there can be an increase of carbonic acid added together could make a small ph drop that should be reversed during the next day cycle.
What I'm thinking and I need to look into this but I have been very busy lately is with you now increases root mass and other factors. The clorine in the pool shock is destroyed when it comes into contact with organic matter. (You should really look into the nasty by products created from this). As this occurs you are losing your buffering capacity.
I would bet that if you switch to h2o2 and added a buffer like calcium carbonate or potassium bicarbonate (which in flower depending on your base nutes may be beneficial) you would no longer see this ph drop.
Like I say I have read up on this to ensure I have it right bit that what's I am thinking for what it's worth
I had this pH drop long before using the pool shock.
I tried H2o2 and lost 1100 plants in under 5 minutes by adding 500ml to my reservoir. Super low dosage. Never again. That was a costly mistake.
So far the pool shock is working great at algae mitigation. And no new symptoms of issues are occurring that werent present all along.
Im going to test increasing the P-K ratio. Everything is pointing to that at the moment. Especially the small/non existent colas. The plants have been getting starved.
Didnt matter which nutrient brand. Raising the EC only exacerbated the imbalance, causing lockout. Lowering the EC didnt result in outright deficiencies but definitely yield loss.
I know Im close to dialing this in. Each run is getting better & better. Many variables have been adjusted many issues eradicated. Just these last few remain.
If adjusting the P-K doesnt work, Im gonna look further into your theory. Heck, Im gonna look into it anyways. But I can only change one thing at a time in this process.