Firstly, Ocean Rock or Texas Holey Rock as some would know it, is not the same as live rock. The main difference is the porosity of the rock, Ocean Rock is no where near as porous as live rock.
Texas Rock is more attractive than live rock to some people. Not only is it half the price of live rock, but it often has lots of interesting shapes and built-in swim throughs for the fish. And lets face it, you have a 0% chance of introducing a bristleworm or some other critter in to your tank if there is no where for it to hide deep within the rock itself.
Before you rush out to buy Ocean Rock, you should consider that some aquarists report that eventually the Ocean Rock started leeching out phosphates and other trace elements. Also, you need to be sure that the rock has not come from a tank that has been treated with copper or any other medicines, some residue is likely to still be on the rock if it has, and that may harm your fish and inverts.
Equally there are many aquarists that report success with Ocean Rock added to their tanks, eventually all the rock turns purple once it is covered in coraline algae, and you can’t see the difference looks wise between the live rock in the tank and the Ocean Rock.
Can you use Texas Holey Rock in your tanks? Absolutely! BUT, you need to ensure you have enough live rock or ceramic media in your tank as well to support your biological filtration.
Live rock, dry rock, mane made live rock… all pretty pricey. But for a good reason. Your live rock provides a home for the beneficial bacteria in your tank which converts ammonia in to nitrites, then nitrites in to nitrates. Without the hard surfaces of the rock, the bacteria will be limited as to where it can be housed. Most of your beneficial bacteria will find its home on a hard surface, very little will be floating around freely in your water column, hence being able to do water changes without reducing your beneficial bacteria.
But Ocean Rock is a hard surface, why is that not OK? Well, it is, to a certain point. It will house the bacteria on the surface of the rock, but as it is not a very porous rock it means the available surface area on the rock is not enough to support the bacteria to its full potential.
What you can do is use ocean rock to bulk out the amount of rock you have in your display, but you need to make sure you have enough live rock in there to support your bacteria.
You can also use 100% Ocean Rock in your display, but you will need to ensure you have highly porous ceramic media in your sump, and plenty of it!
I personally have 50% live rock in my display, with 50% ocean rock to build up the rock scape, I then have a further 5 large ceramic blocks in my sump. This allows for more than adequate surface area for my bacteria to grow on and my water parameters remain stable.
You can buy ceramic media blocks on Amazon here https://amzn.to/2TO3o63
Choosing to use Ocean Rock in you tank is a personal choice. If you prefer the look of it or have it already then by all means use it! It doesn’t hold the same benefits as live rock, but as long as you compensate for the lack of available surface area by adding live rock and/or ceramic media to your tank or sump.