Home Up DIY 10



With the rising costs of setting up reef tanks these days, and increasing pressures from ecological pressure groups. Its fast becoming the case, where the financial costs of fully stocking out a large tank with natural LR can be quite frightening. One way round this is to make your own.

Many of you will be familiar with the Aragocrete method of LR production using white Portland cement and an oyster shell and sand mix.

See here for the Albert Thiel version.

Another recent method that has come to light, is the salting method, which incorporates large granular salt crystals instead of oyster shell. This then dissolves out of the mix as it cures leaving a very porous structure allegedly allowing much faster colonisation, a lighter structure with less water displacement, and an overall higher efficiency for biological filtration above and beyond the capacity of less porous alternatives.

What's the idea then. ?

Well putting it simply, its no more than a mix of Snow Crete (white Portland cement), aragonite sand, and the large granular salt crystals that are used for recharging domestic water softeners. (available from DIY stores like B&Q etc). After making the rocks up, they are left to soak for a minimum 4-6 weeks in plain water which is flushed on a regular basis, during which time, the salt will dissolve out leaving a mass of interconnected tunnels and pores that give  the finished rock a highly porous structure ideal for critter colonisation and bacterial growth both externally and internally. To be honest here, this isn't a method for attaining an instant reef. In all probability it will take a good couple of years even if 'seeded' with 'real' good quality live rock, to reach a point of colonisation on a par with wild rock. So please be aware of this before you start. If your like me and like to stock reasonably slowly, and take your greatest pleasure in watching how a reef matures over time, then this may just be your ticket.

So how do you do it ?

It all depends on what your trying to make. be it individual rocks, stand alone features, complete reefscapes, or branch rock. there really is no limit to what you can do as long as you follow a few simple steps.

1. Decide on what your after, Is it a collection of separate rocks, or a large reefscape made in sections that will butt together to form a single structure, or are you after branch rock, or platforms..?

2. Make your molds.

A: In the case of separate rocks, these can be made in the tried and tested way of a box containing sand that has been formed to create a mould (just like on Albert's site)...

B: If its branch rock your after, then the best way I have found, is to remember that coral branches can and do curve in various directions usually, so initially I make a platform of varying height bricks, blocks, or any other items that take my fancy. I then cover this with a layer of thin plastic, and finally cover that with a couple of inches of aragonite sand. Into this I make a half circle groove in the shape of the branch I want, remembering to taper it slightly as I work a long towards the end for a more natural look. If you can put spurs in as well, then even better, as once set and colonised, it will look to all intense and purpose just like a large chunk of old stag horn coral. You can also make multiple sections which will loosely stack together to look like a very realistic  rubble zone..

This branch was made as highlighted above over a mold of varying height supports, which has a 2" deep layer of aragonite sand (Aragamax) laid over it, and then has grooves made into it, in the shape of the required branch. Once the wet mix is placed along the groves to form the branch, the surrounding sand is gently pushed up and around the mix to retain its tubular / branch like profile. (note the widening towards the end which gives the branch that naturally grown appearance, in this shot the surrounding sand has been moved away after 48hrs hardening to show the tubular profile remains intact.).

The shot below shows the texture (very reminiscent of heavily coralline  encrusted and overgrown natural branch rock. ( this will become porous after soaking for 4-6 weeks)


C: To make full scale rock structures, the process is very similar to that used in making branch rock, i.e. over a suitable mold. This time however, no sand is used, simply a chicken wire and plastic one which will be removed after hardening to leave a completely hollowed out rock structure with a lot of space underneath for hiding filter strainers etc and for fish to sleep etc. The best way I have found is again to make your main structure out of various blocks and bricks etc. Then overlay this with a sheet of chicken wire which you can form and shape in differing directions to give peaks and gullies etc. Once happy, you simply trim off the surplus chicken wire and then cover the whole assembly with a thin sheet of plastic (split bin liners are superb). Now you can proceed to dollop the wet  LR mix onto the mould leaving a nice wide foot print of rock around the outside which will rest on the tank base (spreading the load). To make caves etc, simply leave sections of the mould exposed. Once set the mould can be released leaving gaping cavities in the rock where fish can swim in and out of the structure as they would in and out of the cavities on a real reef.


In these shots you can see the chicken wire frame, supported underneath by bricks etc. The foot of the chicken wire has been folded back underneath. This prevents it getting caught in the setting cement mix which would trap metals in the mix which would cause problems later on. The metal wire should be protected from the setting mix at all times by way of a plastic sheet. Likewise a large sheet should be used to protect the work surface as well.


Once happy, you can start building up your structure by dolloping the mix over the mold, leaving holes etc for cave entrances.

The picture on the right shows a structure hardening off over its mold. as does this small (16"x8"x 8" )island rock made over a couple of plant pots and some plastic sheet. (note the small piece of branch rock behind and the holes left to create entrances to the hollow out centre section.) effectively, These rocks are designed to be placed directly onto the base of the tank with sand spread 'around' them. This gives the impression the rocks are coming up 'through' the sand, rather than being placed on top. much more natural, I'm sure you'll agree.

These shots show a completed structure combining the main rock sections plus separate islands and branch rocks thrown in for good measure. Ultimately, there is no limit to what you can achieve with this method, so play until your hearts content.


How to mix:

Well it depends on what you want the mix for in terms of strength over porosity.  Branch rock needs to be a little bit stronger than plating rock because otherwise it will snap too easily when worked. but the following ratios I have found to work very well so far.

For standard rock structures and single rocks.  1pt Portland Cement - to - 2 pts Aragamax (aragonite sand) - to - 3 pts salt crystals. i.e. 1-2-3

For Branch rock. it needs to be a bit stronger. 1pt Portland Cement - to - 2 pts Aragamax (aragonite sand) - to - 2 pts salt crystals. i.e. 1-2-2

When mixing, Its best to mix up the sand and cement to a consistency like very stodgy porridge, 'then' add the salt last. Once you have added the salt, you mustn't add 'any' more water. .This will ruin the mix and turn it too wet, to the degree that once curing, the salt wont be able to dissolve out.

Getting the best results.

When using the mix, try not to manipulate it 'too' much as this will even out its surface and it will look artificial. I've found that dolloping the mix bit by bit over a mould gives a very natural surface texture. By building up some areas, or by layering over a bed of sand, you can also create ledges and shelves to great effect.

The mix should be covered loosely in an extra layer of plastic for a minimum of 48hrs after you've made your rock, to allow it to cure naturally. Allowing the mix to dry too quickly, will weaken it and make it brittle.

After curing, you should soak the rock in fresh water (preferably RO) for a period of around 4-6 weeks changing the water weekly. During this time you should also monitor the pH of the water. if it keeps slowly climbing beyond 8.3, the rock isn't ready and needs another week or so. finally the salt should have dissolved out sufficiently that the rock is now ready for use.

You may find that for a few months after setting the system up and running it live, that you see a dusty coating on the surface of the water from time to time. If you have any grazers which actively scour the rock such as Urchins or the like, then this dust will simply be some remnants of the anti caking agents left over from the salt. This shouldn't be of any concern. The anti caking agents used in the salt are hydrophobic so wont dissolve into solution and will naturally go to the surface. They represent no physical harm to any tank inhabitants and will quite quickly fall over any surface weirs present to make its way to the skimmer to be taken out as a waxy residue. If large amounts of rock are used then this scenario may continue for some time, but as stated wont represent any danger to the system or its inhabitants.



Fake Live rock and branch at 6 months after seeding with coralline algae slush and LR rubble.


Fake live rock at 12 months. heavily grown over with coralline algae and teaming with life. Obviously corals were introduced separately, but show good basal growth to prove the rocks suitability as a growth platform.


I hope this page has been of use to you.





Home Up DIY 10