I'm using 5 gallon fabric pots with HP Pro-mi...

This is essentially a soilless medium, despite it coming with a light pre-charge around 1EC of nutes. 1) water until 10% runoff, whatever it takes. 2) wait for top 1/2 to 1" dry before repeating. You should be fertigating everytime with a 1.3-1.5EC, well-balanced diet. The runoff ensures that a consistent equilibrium results, which may be a bit higher than your formula, but the consistency is what is important. From there diagnosing and adjusting is simple and fewer other causes to rule out as to any symptoms you might see. Over time if you don't have a formula that works for 99% of plants, try harder :P So, the 10% runoff is incredibly important. Do not skimp on that. It is probably the most important part of watering a soilless medium. If you water at a similar dryback, it will require a similar volume of water, so you can learn this in hindsight only. I use pro-mix hp or bx - whichever is available and cheaper. Consider adding more perlite #2 or vermiculite #3. The "HP" comes with 15-25% or 20-25%... You want it to be ~50%. You'll have to water slightly more frequently, but your roots and plants will thank you for it. It's impossible under any common sense context to overwater a well-constituted medium. the extra perlite or verm will keep it fluffy and airy. Vermiculite adds available Si, too.