There are a lot of ways to grow successfully. This is just what I do. In soil, I give calmag with every non-feed watering through the third week of flower. Basically near the end of the stretch. Starting the first day of week 4 of flower, I switch to a mag sulfur supplement with every non-feed watering. Bud Candy is a weak mag sulfur supplement. There are many others, or you could just use epsom salt. With regard to how long mixed nutes are good for, I just check pH and ppms of the solution. If it hasn't changed much, I'll use it. A few days is usually fine.

I can save u a lot of time, money and disappointment by directing you to a thread on Rollitup, which is exactly like thcfarmer.
The main poster’s name is Buddzbuddha and he is one of the most experienced and knowledgeable growers on the planet.
For the record, I’ve tried his method and it works like a champ.
The basic premise is that most growers, especially new ones like yourself, usually do more harm than good by 1. Getting too many opinions, 2. Rush to fix things, 3. Overreact and 4. End up with 15 bottles of the newest greatest synthetic nute being sold. Most of which are highly redundant compared to all the others.
The grow can and should be simple. You’d be amazed at how little a plant needs to grow adequately. Let that sink in.
Anyway, with this grow, you start off growing your plant in Ocean Forest. It’s good to mix in a little extra perlite, some sort of myco product and worm castings. But that can be added by top dressing later in your case.
Ocean Forest is amended with everything a plant needs and will usually last around 30 days.
During this period, only give water and the routine round of ReCharge or something similar. Water when the soil begins to dry out but doesn’t get completely dry. You do not want to water until you have runoff. Think about it, your nutrients are in the soil and watering to runoff just leaches them out. Also, ph the water to 6.3-6.8.
Depending on your tap water, u may need to add consistent small doses of cal mag.
The plant should grow just fine with this minimal approach.
Once you get to the 30 day mark, or if the plant just looks hungry, you’ll then need to feed it……and you do this by simply top dressing more of exactly what it’s growing in. That’s right, top dress with fresh Ocean Forest, worm castings and myco.
The plant is already acclimated to this environment and is simply getting more of the same.
Depending on the stage of your grow, you may need to top dress multiple times to take you all the way to harvest.
Once you do this grow a time or two, you’ll begin to really understand the how, why and when of growing. You’ll also be confident enough to tweek things and try to put your own mark on the grow.
The thread is over 20 pages with grower after grower asking questions and sharing their own twists.
U do not need a dozen colorful bottles of this or that to grow a healthy vibrant plant.
Anyway, it’s a helluva good thread with a ton of info. https://www.invalid.com/t/ffof-fox-farms-ocean-forest-made-simple-autoflower.996511/
Good luck.

Appreciate the replies guys.

Bull, I began in happy frog + perlite + diatomaceous earth and turned it over for like a week before planting seeds in it. Then moved to 65/35 happy/ocean, then 100 ocean. I use tap water, after bubbling it for 24h and allowing it to sit for another2-3 days. The ppm is around 125-130, but I do need to ph down each time.

I'll give the thread a read tonight. Again thanks for the long reply.

knew2growing said:

I'm confused at which point I should stop using cal mag

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It is confusing because there are many different opinions. I don't use a cal-mag product. Instead, I use gypsum (calcium sulfate) and Epsom salt (magnesium sulfate). I top dress a tablespoon of each about every two to four weeks. I don't stop amending either, but I do watch the leaves to see what the plants need.

I'd say one of the best, first decisions to make is whether to use synthetic or organic nutrients.