Reuse of old coco is fine?

Why did you kill your old grow??? If it had anything to do with a soil pathogen disease or pest then you will also need to sanitize that medium. pressure cooker works well or an oven. Good Luck.

I wouldn't do it, it is cheap and easy to use fresh coco coir. The risk of disease and/or contamination is just not worth it. With all the expense involved with growing, not to mention effort, why risk your entire grow by trying to save a few dollars? Just remember, - quality in = quality out!

It doesn't hold cal/mg well so don't worry about that, just add a little when you start to feed after they sprout

As others said, but when you give it that good rinsing do it at 5.8 ph water

@Masino_delgrado a good rinsing and it should be fine mate chuck in fresh perlite for aeration

Absolutely.. older coco is usually better because it’s been well buffered from the previous feeds.