Who Gives A Fish Forums

hey all,
found this elsewhere and thought, why not? been spending a small fortune on rocks and sourcing from everywhere (read: 'borrowing' from mates' tanks).

So, apparently you can make your own rocks using Portland cement and play sand. The cement's the key - it's got calcium silicates and sometimes iron, aluminum, and magnesium in it. Just make sure you get it from a reputable supplier and it's safe for aquarium use. Type 3 Portland cement's the way to go, but 1 or 2 will work too.

Here's what you do:
1. Clean the play sand if you can be bothered (it'll make the rocks stronger, allegedly).
2. Mix one part cement with four parts play sand - it should be all pasty and whatnot. Use gloves, or you'll end up with alkali burns.
3. Fill a container with damp sand, dig out holes, and you've got a mold.
4. Add the cement mix, shape it up.
5. If you want caves or tunnels, use more damp sand.
6. Leave it alone for at least 24 hours.

Just sharing this, no promises it'll work, and don't come crying to me if it all goes wrong (see you in court, mate).

I've given it a go in the past, about seven years ago for my reef setup. No issues whatsoever, but I'd definitely recommend letting it set for a couple of days, 48-72 hours to be on the safe side. Then I'd soak the rocks in water for a few weeks, changing it every couple of days. This process really helps strengthen the cement and brings down the alkalinity levels of the rocks.

Three questions for you, oakleyride.
Would using coral sand work just as well as play sand, I'm guessing it's the same principle?
If it does work, do you think I'd get a better colour from it, I'm thinking it might give it a more natural look?
And, got any pics of your tank setup, would love to see how it turned out. I'm planning on giving this a go at the weekend, thinking of using coral sand, might be pricey but if it looks as good as I think it will, it'll be worth it.

To be honest, this technique is more suited for hard water tanks. The homemade rocks will buffer the water to some extent.

If you're considering using coflake sand, it's worth noting that it'll give your rocks a much coarser texture, making them more prone to crumbling. Take a look at DIY live rock – they often use aragonite in a similar way.

I'm afraid I don't have any photos, did this ages ago and I've long since moved on to different fish, South Americans to be exact.
If you're looking for the original recipe I used, check out www.garf.org - that's where I got it from, and it worked a treat for me, but like I said, I'd only recommend it for hard water tanks, and I'd still advise letting it cure for a good 48-72 hours before soaking.

cheers for the link mate, will check it out. been searching for the diy rock thread on here but no luck so far. this is for my mbuna tank, so hard water is a plus. if i give it a go, i'll test the water the rocks are in - tap water here is 7.9 so might take a bit longer than 3 weeks to get it right lol

If you're looking to speed up the process a bit, I've found that adding a cup of distilled white vinegar per 5 gallons can make a noticeable difference.

I've never tried it for a 3D background, but I'm thinking of giving it a go, now that I've got my DIY rock plans sorted. Has anyone else attempted this, or is it just me getting a bit too excited about the possibilities?

I vaguely recall a post somewhere about a 3D aquarium background that used polysytrene as the base structure, then someone applied a top coat using this DIY rock method to achieve that natural rock look.

This person made a DIY background using styrofoam and then applied a top coat of cement and sand for that rock appearance.