as your plant pulls hard on P in or around weeks 3-6 mate, it releases lots of H+ ions in to the media, constant application of Potassium high feeds increase the rate of positive ions, this overwhelms the negative charge of soils and media like coco, peat etc etc etc. This is the root cause of all pH climb in late bloom, it is hard to manage in high intensity growing situations but if you want your pH to come down, feed only Anions and lower the input pH range of the solution.
The best option other than having a healthy colonies of both -/+ microbes like bacillus, psuedomonas and mycos, which would begin to store any free ions like the H+ ions, our plants spits out when they consume a P- ion for example, on their tiny bodies, using them as food for themselves, and thus preventing them interfering with the balance of current in our media which is the root cause of pH swings.
Ever changing plant requirements mean we can get the reverse, so where we have an acidic condition, our plant spits out OH- ions which again saturate the media if there is insufficient biology and or humates to scavenge those items of ions added to the soil system by the plant and us the grower.
Everything should be seen as 1 in 1 out mate, its all balance of systems and dont forget, plant balance, is not the same as media balance. The plant does not care less if the media already has an abundance of Cations in the space, it will spit out regardless. Its only care is balancing itself.
Now the media needs help to manage the ions the plants spits out or otherwise these accumulate and get things out of balance, once the media goes out of balance, the plant cant get what it wants anymore, but this is a failure of soil system management eg, not maintaining those things that mop up the garbage. Adding more biology and constantly adding Bio Balance Foliar and More Root Better will help purge the free ions, and help prevent them becoming an issue.
Know this simple truth mate, plants work in cycles of days, and this data of instruction on what to do when is in the DNA of all plant cells. The plants' nucleus directs life processes based on a simple instruction manual that says do this on day 1, this on day 2 this on day 21 bloom for example. If we miss feed our plants, this simply means we do something that has lost the track of the plants innate biological instruction manual, and our media tolerance is low, eg we have low biology, poor humate content, high salt levels, low air rates, then we quickly develop problems. The art of container growing under high intensity set ups is no joke nor is it a small feat when we make it to the end having never seen an issue.
We can do everything we knew worked, get one unruly child and our whole program is questioned. Be sure you have it right mate, you cant win with every plant. But we can learn how to spot when the problem might have appeared and this will help guide us tomorrow to be better. Nothing is every really so perfect all plants be unequal LOL
Bio Balance Foliar and Bio Hydrate will help. Anytime before day 21 bloom you can add Bio Root Juice, we will add this to the store shortly but i will see if Alan has the samples. i did have some but the guys gave them out when i was in greece...gah so I am waiting on him getting new ones ready for you all the try :)