... well, a cheap liquid drops kit will suffice,... yeah, keep feeding her! Organics take a bit longer to get in there, for reasons mentioned above,..... new pics still look mostly P defc. to me,... are you adding Ca-Mg+ in as well?
Enzymes help break down organic matter,... Hygrozyme, Canna Biozyme are good representative products,... they have several enzymes in them that help tackle more slow/difficult matter in there, which helps the rest of the soil herd do their job, which in turn benefits the plants! ...Mammoth P is fantastic stuff, but it's not an enzyme product (sorry brudda Fairly!), it's a specialized brew of microbes that focuses on P and micronute turnover and availability, different from the usual myco's and other beneficial bacteria's in other inoculants,...
A TDS meter is only about $10,... decent pH meters about $30-50, cheaper ones are around, but are dubious for accuracy after a while,.. good meters are sensitive instruments, and need proper care...storage solution, and calibration solutions 7.0 and 4.0,.. some come with calibration soln., and storage is readily available too, not expensive,... storing them right is KEY,... dry electrodes will cause bad readings and eventually ruin them,... I also highly recommend the Accurate 8 soil pH probe, for actual
in-pot pH measurements, nothing beats this (run-off testing is crap usually).. I know this all sounds $$, and confusing, a PITA too,.. but you can avoid so many problems right off the bat by monitoring your water and nute soln. inputs, so the soil doesn't get out of proper pH range to begin with,... fixing off-pH soil is a real beating, costly in time labor and sometimes products,...and more importantly, plant health.. stunting, crap yields, makes some grows a waste of time and $$!
Another fine alternative to consider is Mephisto/GBD's super soil mix for auto's,.. all you do is buy a good base soil (like Roots Organic), mix in the super amendments, fill half the pot with it, top with reg soil on that, and it's water only from there! Sometimes, you may need a little boost of something, usually P-K during bloom, but that's very conditional, many don't need it,...lots of fine grows here using this simple KISS system! All I'd add to that is a Si supplement, enzymes, kelp extract, and have Ca-Mg handy just in case,...