Smiles here! Use that dosing calculator I posted and keep a long. I'm old school on dosing alkalinity. I dose baked baking sofa (because I always need a bump in ph) and mix it into a gallon of RO/DI water and drip into my sump overnight. Slow drip. I test for alkalinity twice a week, dose as needed and keep a log. Keeps my alkalinity around 8 dkh. Dose no more than 1dkh per day and your tank will be happy. I also use kalkwasser (pickling lime) in my ATO.
Most likely you will need to clean your pumps and heater of perception from calcium. Bath in vinegar works well.
Your calcium most likely will be low now. If your alkalinity is stable, dose calcium till your back at 450.
Good luck and go slow.