@Tim Fox
Did you ever say WHAT you were feeding it?
How much?
How often?
The plant looks like an Auto with it's shown problems (common in auto's).
Auto's can be quite fussy. I don't do auto's and even give away the freebie auto seeds......I don't have time for them..
Wow, The answers for pH in soil are not the best....
First off you listed Si as being used....That is a powerful pH up...Not only that, Si is already IN your soil.....The use of Si in soil is not a big need....It's more a Hydro thing as 98% of all nutrient lines for hydro don't have enough, they can't. Si must be separately bottled. Si reacts with the bottled nutrients and creates lock outs (I suspect that is where yours came from. By adding what was not really needed/ causing an excess-blocking out Ca, Zn, Mg and allowing too much P. You MUST add Si first to your water and mix well before the nutrients as this will many times
cause those lock outs).
If cared for right, even synthetic runs do not need to be pH'ed in soil. Soil self pH's.
The pH of the run off is NOT the pH of the soil! It is the pH of the run off and while you can learn to GUESS the pH of the soil from the run off....it will be a hit or miss thing for several reasons. pHing soil accurately is not easy with the low end meters you get in a grow shop.....The REAL pH meters used by those who REALLY need them cost over 1.2 - 4K each! Getting the same reading every day is next to, if not impossible!
When you water soil grows. The pH will swing sharply one way. As the soil dries it swings back the other. (Natures way of allowing for the best uptake of available nutrition from that pH scale above). Now then, to get that "same reading" day to day. You would have to take it at exactly the same time and water at exactly the same time. The temp would have to be exactly the same as would the RH in the grow......Each of these factors effect the soil's pH from small to large amounts.....How do you get consistency in soil? The soil it's self supplies it to the plant as it needs it by bio interaction between the plant and the soil.....
Do not "flush"....You can cause more problems faster then fixing a pH lock out....Simply water it out by watering plain Ph'ed to 6.5 water with some of that "zyme" in there for a week to 10 days in veg or early to mid bloom. You will look for the "fix" in the new growth being healthy and normal......Damaged leaves never revert to normal. Only N problems in leaves "recover".
Unfortunately, your near the finish. Your best bet is to simply water it with that 6.5 water till harvest and call it good.
When you transplant the seedling into your chosen soil. Add some Myco's to it. Use a "zyme" product like from Canna or Hesi. Most nutrient makers have one. They will keep that micro heard of bio's in the soil there.....This will help the soil pH it's self.
If you feel you must pH feeds and waters......simply pH all ingoing to 6.5 and forget the pH of the soil!
FFOF is a fair soil....I don't like it.....to many pests come with it sometimes.....They do make it from wild forest soils and add things.....The wild part is were the pests come from...not all the time,,but to damn much for me.....I make my own water only SS and go from there.
If you do choose FFOF,,,,,add some Oyster shell at like 1/4 cup per cubic foot and mix in well, as I don't feel the dolomite they add lasts long enough. Dolo is HIGH in Mag and fast release. So let your plant dry out pretty good between watering/feeding to help reduce the Mg uptake a tic...Oyster is a bit more long term and will help better with pH control..
FFOF is light on Perlite. Add about 1/8 to 1/4 by volume...
Doc
Ca begins to lock out below 5.9.