1-It's not going to hurt them if I put them in the 10 gallon until the sand settles I've heard it can take up to 7 days to fully settleOh! Well this changes a lot! I'm assuming the 36 is cycled. The substrate change is relatively straight forward. Empty about 40% water, net fish and put them in an already set up tank (put the filter you are using for the 36 on the 10). Take out decor and plants and empty the water and substrate. Give the tank a nice wipe with paper towels (don't use windex or anything), and prepare your new substrate. For a 36 I'd recommend 2 bags of Quikrete play sand. Its a bit overkill but will let you have what you need, and ensure you have enough after washing. The next part is super important, you need to clean the sand. A lot of times the sand is really dusty. When you go to get the sand (or if you already have one) get a nice big bucket (rinse it out first) and pour the sand in. Then swirl it around and run the water through it till the water is pretty clear. Put the substrate and decor/plants in and then fill and add fish. You are set.
2-do I still have to size down on fish
3- any tips on plant and decorations to help the Cory's?