polystyrene and concrete background

[Midas]

Here is a pic of my effort at a polystyrene background covered with a layer of concrete.

What do you think?

[Vip]

thats a background? all those rocks on top of each other?

[crazyfishlady]

looks awesome!

[Midas]

Originally posted by Vip
thats a background? all those rocks on top of each other?

They are not rocks stacked on top of each other, that is just what I have made the background look like. What I did was sculpt individual pieces of polystyrene into rock shaped pieces and then siliconed these together. Then I used a coating of concrete on top to try to make it look like rocks stacked up on top of one another.

There are several holes for fish to hide and they can also get in behind the background to hide if they want to. They seem to like it.

It took about 2 months for the pH to settle down enough to put fish in (pH was high >9, due to calcium hydroxide from the concrete). I was doing 100% water changes every week for a couple of months. The concrete is still causing a slight pH rise, but I am countering this with addition of hydrochloric acid to maintain a pH of 8-8.2 (tap water here is very soft (GH&KH ~40-60mg/L) with a pH of 6.8-7.2). With the help of the concrete the GH has come up to about 100mg/L, and I'm using sodium bicarbonate to buffer up the KH to about 100 mg/L also.

[Seedy]

Looks great!!! But I would never recomend concrete in an aquarium....judging by the trouble you've had, I think you understand why...

Isn't there something that you could 'seal' the concrete with?

[Midas]

I think there are compouds that you can coat concrete in. However to seal it completely it would be quite expensive if using something like a resin or some kind of plastic polymer.

Since out water is quite soft I figured unsealed concrete would be one way of raising the hardness. I wouldn't recommend concrete for anything other than a high pH tank, such as Africans. It would be too much of a headache to keep the pH under control. The rate of pH increase that the concrete is providing seems to be getting smaller all the time though week by week. Give it a year and it might not even be noticable.

[WineTechie]

Love the tank. How long did you let the concrete cure before putting it in the tank? How thick of a layer did you use? Did you tint any of it, or just leave it natural? I assume most of the brown is algae?

[Midas]

Thanks

I let it cure for a few days before putting it in the tank, keeping it moist in the process by daily spraying of water. As I mentioned above, it was 2 months of 100% bi-weekly to weekly water changes before the curing process slowed enough that I could put fish in.

The concrete layer is about 2-5 mm thick. I didn't tint any of it, but if I did it again I think I would try and do something with the colour. I thought maybe about putting some black sand in with the concrete mix to darken it up a bit (we have black sand beaches here 5 min down the road, so it is readily available). Yep, you're right about the brown, its just algae. Something I have just recently noticed, the algae seems to be getting into the pores of the concrete with time and the pleco can't get at this stuff in the pores. This is darkening the concrete giving it a more rock like appearance over time.

[Midas]

An update if anyone is interested. I am now no longer having to battle to keep the pH down with addition of acid. The pH now seems to actually decrease slightly over time without any help, so I am now having to buffer the pH up with crushed shell and sodium bicarb to maintain a pH of 8.