I always water with 6.5 pH don't know how the runoff pH was so low and was still growing, maybe nute lockout out of no where?..I can use the general hydroponics pH water tester solution to check the runoff as well right? Just want 2 make sure I'm using the right equip
Ignore pH and stop washing the nutrients out of your potting mix. Read my post #19. Not to rain on your parade but I'll give your plants 2 weeks at the rate you're going and they'll be "toast". Trying this and that hoping something sticks will further result in a decline of plant health. You're well on the way thanks to the use of the bloom food.
There is no way your ambient soil can have a pH of 4.0 unless you're planting in pure peat and adding sulfur. Along with shit canning that bloom food, toss the pH meter and get a quality Hanna WITH calibration fluids. Calibrate before each test.
The proper way to test soil pH is to add a small amount of soil to a clean jar, one that has been rinsed with distilled water, add
de-ionized water to the jar, shake, let settle, and stick yo probe in. Amounts of water to soil is irrelevant as the water is de-ionized and will have no pH value as measured by your pH meter. Buy the water from a lab supply store or do what I do, ignore soil pH. It's one of those things where folks don't know shit, act like they do, do the RIU pH-n-Mg dance and you're stuck with failing plants because you listened. You're most likely over-correcting that which did not need correcting in the first place....slippery slope.
Also, I doubt if you have a Mg deficiency. Most would not know what to look for regarding the lower leaf chlorotic Mg symptoms. What's "I gave them a little epsom salts" mean? You do know that by over-doing one element you're creating a deficiency of the other? Get familiar with the concept of "nutrient antagonism".
You need to get back to the basics, learn how to grow a tomato, and unlearn all the crap that is presented in RIU. You'll thank me for my forward approach once you see the light.
Good luck,
UB