I have used some of the "recipes" found online. I made about 250-300lbs of rock. Some of it is in my system now. I wouldn't use anything but #1 Portland cement (its a white cement). I even got creative and added a few of my own "ingredients" to experiment a bit (crushed clam shells collected locally, crushed lava rock). Most of the formulas call for some type of Arragonite. I have used different size grades of arragonite from sand grade to #15 (#15 is very course, from 1/2" pebbles to 1"). It takes a lot of patience to make your own rock. Mine took 10 mos of RO water soaking, vinegar baths, and if you're adventurous and careful...muriatic acid baths. Not to mention a 24hr dip in the Long Island Sound! All of my rock is starting to color up very nicely. The only thing I have noticed, and I'm not sure if it's because I pulled my turbo snails out, or if the rock is leaching some phosphates...but I have a little algae growing on the rocks. If it is from phosphates, I could have done a Lanthium Cloride bath to remove them. The algae is not bad though.
I have to tell you...MAKING THE ROCK IS A LOT OF FUN. Time consuming, but fun.
The other thing I would have done different, is to drill (with a masonry bit) random holes in the rock before it goes in the DT for plug placement. Its easier than gluing. IMO.
Good luck with it if you decide to take this journey. If you have any questions, PM me. I'll see if my experiences can help you in your venture.
P.S.- Like I said earlier, it takes a lot of patience through the "soaking out" period. YOU DO NOT WANT TO RUSH THIS! Portland cement has a natural pH of 14. You will kill anything that is put in the tank if you dont soak out the pH buffers.