3 cups portland white cement, 1cup oyster shell, 1-2 cups rock salt, just enough water to get a good oatmeal texture. let sit in play sand mold for 24 hours, soak and rinse weekly till phosphates are in an acceptable range.
use the semi fine play sand to make molds to pour the mix on so you can make shapes you want, just make sure to dampen the sand enough to hold its shape. it leaches phosphates because of the cement mix, eventually (over years) the concrete will completely break down, its just what the salt water does to it. i soaked mine for about two months before the phosphates were down enough.
No it won't, well it should not anyway, but that is one of the issues with "cheaperized" forum recipes. The issue of phosphates is not an issue at all, unless you use a "cheaperized" forum recipe.
If you want to know the real recipe, it is as follows:
1 bag sea-flor grade ARAGONITE "sand."
1 bag Aruba shell ARAGONITE "gravel."
1 bag RIVERSIDE low alkalinity white cement.
2 - 3 cubic feet of plastic sawdust (go sweep up for an acrylic fabricator.)
a bucket of water (5 gallons) or two if you want to clean stuff up.
The sand and cement mixed dry, and then water added to just get it to an oatmeal consistancy (the only part that has not been "forumized.)"
The Aruba shell is used for the mold.
The correct mixture is (using measure devices of previous poster):
5 cups ARAGONITE SAND.
1 cup cement.
1 cup plastic "sawdust."
Produces a predictable 6 - 8 week cure time, unlike the "forumized" recipes whose real cure times can well exceed 1 year to never.
Notice the differences in the ratio of sand to cement, and "oyster shell," to cement; a ratio of rock salt that is way off the wall. The "right" brand of cement is Riverside, not Portland, with a very low alkalinity (the only issue there should ever be with DIY rock.) There be differences, but I am not going to do a dissertation on it. Sorry to say, home depot and big box stores don't have it.
Basically, the cement/oyster shell/rock salt "rock" is a block of concrete chock full of phospate laden chicken feed oyster shell, (depending on where you get it) but it is also very very alkaline which is a bad thing, (unless you are culturing cichlids) and rock salt. Who would want that in their tank in the first place is beyond me. Playsand has oil, and heck knows what else is in it, having been stored in piles outdoors, and oiled to keep it from blowing away....sometimes I think folks just don't put enough thought into what they do and suggest others do, but at the same time I know it is sincere and well meant.
Incidentally, you are not making live rock. You can't make live rock; you can make base rock, throw it in the ocean and it may become live in a couple years, but that won't happen in a closed system: bacteria and some algae, don't make a rock "live." Well there are things you can do if you have the patience to culture the rock, and have good seed stock.
Yep, what he says is true. There are many different pros and cons for many different things. The way I did it is easily the cheap easy and probably not the best way but it will get you rock in your tank. Honestly the best way to get rock in your tank is to just get some dry rock that is meant for marine aquariums. By the time youve done all the work with either recipe Im betting youll wish you had just gotten some new dry rock (speaking from experience here). No matter what recipe you use or ingredients you still probably wont end up with rock that really looks correct, or reacts correctly in the tank chemistry.
It often depends where you live though. When I started my tank a decade + ago I used almost exclusively home made rock, using the GARF recipe (similar to what Uncle posted but, I used portland cement though, as that was all I could find) Never had a phosphate issue or Alkalinity problem with it, but it was damp cured for 2 months then cured in water fed fresh from the dehumidifier in my basement for another 2 months. Still have about 50 or so pounds of it in my tank and it's held up really well over the years. Incredibly porous compared to normal live rock, which can be good and bad. Good in that it supports a ton of beneficial bacterial and all sorts of other little worms, pods, and critters, that normal rock wouldn't, but bad in that it can potentially be a sink for nutrients (a problem I've never had).
In my case it was about 1/4 the cost to make my own base rock compared to mail order. But now I can buy dry base rock and sometimes live rock at the local fish store here for about the same cost. (that wasn't an option in Northwest Iowa a decade ago when I had to make a 5 hour round trip to get to a store that sold decent saltwater livestock and supplies. The gas alone made it worth making my own out of locally available reef substrate and portland cement (the Earl May garden center next town over, of all places sold aragonite sand and crushed coral even though they didn't sell saltwater fish).
While the cement choice may or may not pose a problem, you absolutely do not want to use any aggregates that are not "reef safe" or otherwise inert. Or as Uncle pointed out you will run into problems.
Even if it's not cheaper, it's a lot of fun for me anyway, and you can make pieces that suit your specific needs. For a tank that will be totally full of coral you'll never know the difference, but for a new less stocked tank or a FOWLER you'd always see the rock and it would not look quite right IMHO.
Much of it was covered above, but the key to the hanson method is sealing the cement. I don't find polygem 1319 in "home use" quantity though... we're not exactly saving money by spending nearly $200 for a 3 gallon jug. Maybe a cleaning/flooring/contractor could score a quart or gallon size container?