Concrete bottom - an alternative to sand bed or bb

mxett · #1 12/15/2007, 05:54 PM

I'm soon to set up a 4foot x 4foot x 2foot tall tank. I haven't been very happy with ssb's I've used in the past. They collect an unbelievable amount of detritus over time.

Waste I'd rather not have in my tank.

For the last 6 months I have tried bb with a rdsb, with some good results on my current 90g. I'm not really that keen on the look however. A glass base just doesn't look 'finished' IMO.

On my new tank I am seriously considering a 2cm (3/4 inch) white concrete base. I would put plastic on the bottom glass, some inch wide foam around the sides (so the concrete doesn't touch the sides and possibly crack the glass if it adheres to the sides and shrinks or expands when it dries) and then pour and set the concrete directly in the tank. I would then add some features using some more concrete over the original concrete base once it has set, to add bumps and valleys and a more natural rocky appearance. Then after it all cures I would add base rock over it, then add the live rock I have in my current tank.

To cure the concrete I would partially fill the tank with water and let a powerhead distribute the flow continuously. I would replace the water every week, then test the pH until it comes down to 8.5 or so.

Any thoughts on this idea? I have seen a website where someone has done a similar thing and it came out well. Anyone on RC tried it?

Thanks

seagirl · #2 12/15/2007, 06:15 PM

why not use some colored hdpe if you don't like the glass look? i have even seen people use corian countertop material. I would neve use concrete in one of my tanks, but thats jmo.

Whisperer · #3 12/15/2007, 06:41 PM

Sounds like a good plan. I, too, do not like the look of the BB. I have thought about the idea before but couldn't do it because I would need another large tank to hold my animals. I just want to comment on the styrofoam edging. I think, over time, it would crumble/disintegrate. However, I think the expansion/shrinkage of the cement in this case would be negligible given that you aim to achieve a stable temperature with narrow swings. I would worry about the coefficient of thermal expansion when you are close to boiling or freezing. JMO

Fish&Corgis · #4 12/15/2007, 06:41 PM

I just put in a concrete pool this summer. While the concrete cured I had to add muriatic acid to keep the PH in control. I am not sure what it throws off when it cures, but you will need to do a lot of water replacements.

m2434 · #5 12/15/2007, 07:33 PM

Concreate rocks are common, so I would be fine, but the rocks do take a long time to cure... I think it would look great if done right.

You might try Aragocrete.

mxett · #6 12/15/2007, 08:16 PM

I do not intend to keep the foam edges in place, Just in long enough until the concrete sets, then I would take them out. Yes this would leave an inch edge around the sides. I might place rocks or maybe sand (lol) around the edges to smooth it off.

I have even thought of creating a replica 'cast' on my garage floor and laying the concrete, creating the variations, and even placing the base rock structure, outside the tank. I would use dividers to make say 2 foot pieces. I could then cure the pieces before placing them in the tank. If they were 2 foot square, or even 1 foot square, I could then build them like a jigsaw puzzle in to the tank when ready.

As far as the pH goes, as m2434 said, these DIY concrete rocks are widely used with no problems.

Whisperer · #7 12/15/2007, 08:25 PM

I was thinking of the same thing. Like making slabs and fit them like tiles. This way, I won't have to cure it in the tank itself. I just thought of a potential issue down the line...it will be covered with coralline algae (at tleat the light exposed areas). I do not particulary like a pink floor

mxett · #8 12/15/2007, 08:39 PM

Quote:

Originally posted by Whisperer
I was thinking of the same thing. Like making slabs and fit them like tiles. This way, I won't have to cure it in the tank itself. I just thought of a potential issue down the line...it will be covered with coralline algae (at tleat the light exposed areas). I do not particulary like a pink floor

Atleast it will have texture and form like rock. Much better than just glass. Plus, you can glue and attach all sort of corals in all sorts of positions, not just on glass. If done artistically the possibilities are endless.

jman77 · #9 12/15/2007, 09:23 PM

Concrete bottom,

LOL ..... you have an idea of how much CC weighs.

Either leave bottom bare and it will get covered with coralline in time.

Or do a PVC, hdpe, or epoxy. What you are thinking of doing is alot of work, time, and trouble when there are cheap solutions out there .

If you are still wanting to try CC , go the Aragocrete route that mixes sand, shell, salt pellets into the mix, and get the CC mix the cures to a low ph right away so you don't have to wait a long time.

mxett · #10 12/15/2007, 09:33 PM

The layer would only be thin. I saw a comparison of the weight of concrete to just sand, then rock. They were all very similar. I intend to have a fairly open aquascape aswell so I think the total weight would compare, or maybe even less than a heavily stocked 'wall' reef with a dsb!

mxett · #11 12/15/2007, 09:34 PM

What cc cures to a low pH straight away??

kuyatwo · #12 12/15/2007, 11:58 PM

on my friends take i dont know what happened he was dosing alk as it was too low and somehow it melted the sand together it is really cool in my opinion...but his sand is all one piece of rock now

SuperNerd · #13 12/16/2007, 12:03 AM

what about that material some of the europeans use? I'm not sure exactly what it is, but it's light enough to put on the sides of the tank and appears strong enough to support corals on the sides of the tank as well.

King-Kong · #14 12/16/2007, 11:07 AM

2 part clear-drying epoxy + sand will be easier and give you less hassle.

I took mine out, though. I've got the panels sitting outside (from the 90g AGA RR). Just went with standard white starboard about a year after the epoxy.

It sure looks realistic, however:

bawla47 · #15 12/17/2007, 11:28 PM

whyd you pull it king kong? did corraline start to grow ?

mattsilvester · #16 12/18/2007, 06:30 AM

concrete - when wet is approximately double the weight of water..... so even when wet, 1" of concrete weights what 2" of water would.....so once dry, its maybe 1.5 times ????? Bascially, I wouln'r worry about the weight, unless you ever want to move teh tank afterwards, which I think would be impossible withotu breaking it.

I think its a cool idea to be honest - if you are confident that there will be no effect on water chemistry.....

The idea of bedding some base rock into it strikes me also..... if you know what and where and how you are going to aquascape it, it would be a great idea to stick in some "columns" to support the structure......

Its gonna look wierd, but cool, I think...... you mention a website where someone has done something similar..... got a link?

boxfishpooalot · #17 12/18/2007, 07:19 AM

I am not sure what it throws off when it cures

mosty calcium hydroxide and silicate. As well as any heavy metals present in the mix.

King-Kong · #18 12/18/2007, 08:15 AM

Quote:

Originally posted by bawla47
whyd you pull it king kong? did corraline start to grow ?

Well, first I suspected it was the cause of my abnormally high silicates; it still may have been, but I never really tested well enough to know.

The other major issue was that I just didnt cut the boards properly, and left thin, tall cracks that let detritus settle, but didnt let flow through.

Eventually it got covered in corraline anyways and you could only tell what it was in the truly dark/shaded places.

I eventually replaced it with standard starboard, bevelled, and with more space between the side glass and the surface. No more poop settlin' for me!