In the left sidebar or towards the bottom of any page is the TFP Wiki that deep dives many subjects. Scroll though anytime you have a thought and it's likely we'll covered. And then work you way through anything relevant to you in your spare time. Good stuff.
In this case, checkout PH, TA and PH/TA relationship.
Ok GLAD I mentioned it. We often get spun around when a thread is pages and weeks deep. (Can't remember everything about everybody).
So when you raise your CYA, you also raise your slam FC target. (+4 FC for every 10 CYA). If algae was starting unbeknownst to you because it's microscopic and you can't see it until it's a runaway train, you might raise the CYA only to find out you have a way suckier slam in the near future. So when adding substantial amounts of CYA, like getting to SWG level here, then run an OCLT first. If you pass, then add away, and if you fail, slam before raising.
That's +250 and you only need to get to 350 total, not 450. What's the CH of your fill water ? If its high like most in your area, 250 to 300 is fine and it'll rise quick on its own, so add 50 to 100. If the fill water is softened through your home system, then aim for 350. (+150).
I'd personally do 10-ish pound batches if adding alot.
