Hi all is Crush Coral the same us Crush sand do they both raise your KH to put in a media bag to go in a external filter please

Crushed coral sand is the same as crushed coral and will raise kH. You will need to do smaller water changes though as coral takes a while to buffer the water so kH will drop when you add new water and take some time for the coral to raise it back up again. That means swings in pH so smaller water changes to prevent too big a swing.

If I do small W/C it pulls the KH down more because I use straight tap water which shows on the reading there is no KH in my tap water so won't It be if I do more W/C THE MORE KH I will lose in my tank water

If you have no kH at all in your tap water you'd be better off buffering the tap water rather than trying to buffer in the tank. This will do the trick: https://www.ebay.co.uk/itm/Seachem-Alk ... m:mkKkBCL7iAkoVvbzOqdeJeA