Ro water

[DBS83]

Building a new tank set up display 275 gal and sump 125 gal I am adding a auto water top off connected to a ro unit I will be adding crushed coral to the sump was wondering if their is any other rocks to add to bring the water back up to a more hard level location is texas also live plants are going in the sump and I am trying to build a complete eco system to live and thrive starting off is shrimp not sure what type yet 

[Mmiller2001]

We need more information. What kind of fish? What specific GH and KH do you want? Why are you adding crushed coral? What kind of plants?

Being more specific will help you get to the answers you are looking for.

[Patrick_G]

With that caliber and size of system I’d be thinking about a water holding tank with water pre-mixed to your requirements. 
 

[DBS83]

The crushed coral works well for my snails and shrimp I tryed many times to keep them in seasoned aquarium and no luck untill I added that. plants in the sump will be a Java fern and that's the only one for sure I know of I am still planning the rest of the plants display tank I have 2 African side neck turtles going in and still planning the rest of the tank the reason for the ro filter is in my area the water is horrible with the ro unit the water actual becomes usable so as a precaution I was researching what needs to be added gh and kh I was looking for 100 to 200 ppm that should cover most species

[Andy's Fish Den]

Texas holey rock, any of the rocks used in saltwater tanks will slowly dissolve and add in hardness. You can always do the acid test on a rock to see, pour a little bit of vinegar on the rock and if it bubbles it will raise the pH and hardness.