I added mycorrhiza to the coco coir from a local store. It turned out that there is slow release fertilizers in it. Was not indicated on the packaging.

Whats the runoff like when things are going well and happy/healthy? if you don't have this baseline, don't overreact to what you read with runoff or soil slurries. Consistency in how you measure will drastically impact what you see. these measurments are not accurate to what is actually going on in the substrate. They correlate and help, but without a normal baseline value to expect, you have no idea if there is actually a problem due to this vs just ratios of nutes and total concentration fed. Drainage water? rain? Don't use that. It's a myth that it is 'better' for the plant. All it does is risk exposure to whatever pollution is in your area. Rain water is often very acidic, nowadays. Flushing should be in response to catastrophe. Soilless is easy. Fertigate everytime with 10% runoff or more. Wait for top layer to dry and repeat. Later on in flower, you can increase fertigation with a robustly grown root system if you follow these simple suggestions. This avoid superficial roots and maintains a very healthy root zone. If pH drifts or shifts, blame the fertilizer. Good soilless/hydro fertilizer should be pH balanced and buffered to avoid pH drift. It is also 100% plant ready/availabale. Myco in this context will provide virtually no benefit except the negative of damaging roots slightly. Also, 50+ ppm of P is probably going to inhibit its growth, anyway. Myco is possible useful for soil because it helps breakdown sources of P for the plant. This step is totally unnecessary if you are using the appropriate fertilizers with coco, a soilless substrate. These ratios are ballparks that require adjustment, but at least gives you a solid starting point: 1-1-2 NPK ratio (weighted average relative to dose/total dose of each product dissolved in water, assuming american label standards) 4-2-1 KCaMg ratio Total concentration around 1.3-1.5EC, possibly higher in cases of elevated CO2 and optimal environments. This is going to match growth rate demands so that you don't have major buildups over time. If you do see signs of toxicities, you reference notes and history of formula, adjust in an intelligent way and hopefully avoid the issue next time... avoiding any less drastic dilution or even flushing of substrate. Flushing slows plants down. It's stressful. Do it only when necessary, and following these suggestions should only require minor adjustments vs "oh, shit, it's a dumpster fire!" type problems requiring a heavy flush. when you have a good baseline of what to expect from runoff water, and understand the normal volatility of it, then it can be a helpful tool, but will never be a very clear picture painted from that alone. Good fertilizers will provide pH stability. Lesser soilless fertilzers will result in pH drift. find something that doesn't give you this needless headache. the ingredients in these products are not unique. they are commodities and cheap. Don't overpay for simple things. It's like buying Advil instead of the generic ibuprofrin... zero difference, in this case. there are various optiosn to supply npk et al obviously.. just a loose parallel. So, if you think you overdosed, give 1 normal irrigation with 10% runoff with plain water. Mix up relative to suggestions above in 1.3-1.5EC range, excluding wahtever your tap water provides, and practice good soilless watering habits. Don't let it sit in its runoff. that would defeat the entire purpose of the runoff. take notes. adjust based on what you see. Wthin 1-2 cycles you'll have a formula that works for 99% of plants relative to your local environmental variables. Seldomly worry about deficiencies nor toxicities... such things should be rare after just 1-2 grows and damn near never once you are more experienced with it. i've never measured runoff. I haven't measured pH in years, but do keep some strips just in case. My fertilizer taks care of pH. Runoff is too volatile to trust. Even the rate at which you added water might affect what you see with runoff. My plants are healthy seed to harvest - some late senescence is possible... but never anything that progresses significantly or requires any significant mitigation. you know, drop a fertilizer part by .1g/gal and carry on without a concern type thing. Avoid the self-inflicted pH headache with the ferts, trust me. in mean time pH balance to even it out as best you can.. white distilled vinegar (acetic acid) is a good ph-down option. In short term you can use baking soda for pH up. Over 2-3 months the Na added from baking soda can't do any damage, but might with any long-term mother in a pot. LOL, i use softened water for 3 years now with no issues. Used to lug gallons of it from outside hard water tap... zero difference since that change. Rain water is gross, just a reminder. "Natural" does not mean better and just as often is not.