In future runs I want to get some sort of potassium silicate product (Aquashield/Silica Blast), they make cell walls stronger and are supposed to help the plant cope with environmental stresses such as heat and under-watering. Also, if I get an RO system I'll be getting a cal-mag supplement.
Cool. Awesome with all the hook ups. I hear the Great White is... well... great...
I've been using DynaGro Pro-Tekt as a Potassium Silicate supplement. I think Silica Blast is Sodium Silicate (sodium metasilicate) which I'm pretty sure I avoided because of Na build up being an issue in Coco. As Potassium Silicate supplements go, the Pro-Tekt is the best bang-for-the-buck I found. AN Rhino Skin is another option but much more expensive.
I'm really digging the stuff. Definitely a noticeable difference in the strength of the leaves and the thickness of the stems. I think you'll like it. 3ml per gallon is about all you will need.
I'd also suggest a rooting supplement to assist your root zone health. Something like Rhizotonic, Humboldt Roots, G-Rex... That'd all be good stuff. Whatever you pick is going to be a bit expensive, but when you break it down by plant, and then by gram... The benefits of having a healthy, well developed, root zone cannot be undervalued at pennies on the gram. Try to think of it that way. A $60 bottle of something might seem like a lot, but if you use it on 12 plants and increase your final harvest by just 10% the bottle has paid for itself. I love Rhizotonic!
The Magnesium deficiency usually arrives when the Potassium buffer is over filled, as these elements will compete for uptake. Coco provides Potassium and retains the salt, and once the media is enriched running high levels of K can have a very detrimental effect on the plant. Same thing for Calcium, which also competes. Keep your eye on the Potassium and make sure you don't run too much bloom stuff, especially early in flowering. Keep those N levels in a proper ratio and the PK lower until you're 5 weeks or so into flowering. That should help keep Mg deficiency as a result of nutrient toxicity to a minimum.
I think it's a good idea to start incorporating 10% to 20% strength feedings when you need to water daily, or even every other day. Do a full, then a 10%, then a full, then a 10%. Feeding at full on a bi-daily basis can result in build up quickly once the media has been charged with elements. This can be especially problematic during the 3rd and 4th weeks of flowering. I'm sure you'll be alright though.
I'm blessed with awesome tap water. Well water. The pH at 7.3 and the ppms <60. You on the other hand might have some hard water, given the high pH I'd guess a lot of Calcium bicarbonate. If you know that the K+ level isn't too high and you start running into Magnesium problems it'd probably be good to switch over to RO filtered water (especially for later in flowering) to keep the total amount of Calcium in the system appropriately within range.