Tnx guys I've done my research and pass by some calcium carbonate powder online, how many or how often should I give my Leo calcium? And im still planing to get one
You've shared on your profile that you are 14 yo. That's a good age to get a leopard gecko for a pet.

Thing is there are many care sheets "out there" all claiming to be "proper" for leopard geckos. From what you've posted on Geckos Unlimited, I have no idea what type of advice you've read.
I am happy that you are researching first. :cheer: Some first time leopard gecko keepers buy the gecko and then research.
There's more than one way to raise a healthy leo. However, some things are very basic to all care.
And the seller of calcium carbonate told me that its for aquarium that lower the pH?
You are about to use calcium carbonate for your leopard gecko.
I like to have more information, before suggesting things like supplement dosages for calcium, et cetera. Part of that depends upon the leopard gecko, its age, and its condition. The other part depends very much on the type of insects and worms that you plan to feed your leo and the food you plan to feed those bugs and worms.
In order to maintain healthy bones calcium carbonate and vitamin D3 are necessary. Both too little or too much vitamin D3 can cause MBD (metabolic bone disease) which can be fatal. Vitamin D3, a fat soluble vitamin, sticks around in a gecko's (or human's) system and helps geckos (and us) absorb calcium. Both are necessary either via very light powdered supplement dusting, diet fed, or both.