C.W.
Do you know if it's been sealed? If not, make sure to have that professionally done. It will extend the life of your slate, and you can choose the finish (flat, semi, or high gloss). Shouldn't need to have it resealed but maybe every 3 to 5 years depending on foot traffic. Armstrong Once N Done is the cleaner my husband recommends - it's neutral and PH balanced. You can find in any store practically. We own a carpet cleaning company and we are certified in cleaning/polishing stone floors. Slate is pretty resiliant, but he's a little concerned about the simple green. It may be a little too harsh, just be sure to read the lable to see if it says it's PH Balanced. Armstrong Once N Done is also recommended by carpet stores.