DIY Cement Background won't stop raising tank pH

[EmilyS]

In mid-January I finished a diy aquarium background using this tutorial. It's a 30 gallon tank, but the background only goes up halfway so I only need about 20 gallons of water to cover it completely. For two weeks, I did 100% water changes every one or two days. Within less than 24 hours, the tank pH would go from 6.6 (pH of the tap) to more than 8.8 (max my test kit can read). After two weeks of no improvement, I started changing the water only once a week. At some point, I rinsed the whole background with a vinegar solution, but I didn't have enough vinegar to soak it. I saw negligible improvement during that entire time. Two weeks ago, I got a small bag of saltwater mix. I added about a cup to the tank and left it for a week. There was no improvement, so I added two cups this past week and left it again. A day or so ago, I noticed that the saltwater was eating through my background in parts and revealing the uncolored cement layer underneath. I emptied the tank, rinsed, and scrubbed the background with a brush and then refilled it with 6.6 pH water. Less than 12 hours later, the pH is already back up to 8.3

Any suggestions to stabilize this tank? The only other thing I can think to do is to drain the tank and let the whole thing dry for a week. When I finished the background, I let it dry over a weekend, but maybe that wasn't enough? Any other ideas or advice would be appreciated!

I used the products in the tutorial: Owen Corning pink insulating foam, Drylock Hydraulic Cement, Quickrete Cement Color, and 100% silicone. There are at least 4 coats of cement over the entire background.

 

[PheonixKingZ]

Any suggestions to stabilize this tank?

Remove the background.

The only other thing I can think to do is to drain the tank and let the whole thing dry for a week. When I finished the background, I let it dry over a weekend, but maybe that wasn't enough? Any other ideas or advice would be appreciated!

When you say “finish” what do you mean? What still needs to be done?

—-

If the concrete is raising your pH, there’s nothing you can do to prevent that.

 

[madmark285]

Any suggestions to stabilize this tank? The only other thing I can think to do is to drain the tank and let the whole thing dry for a week. When I finished the background, I let it dry over a weekend, but maybe that wasn't enough? Any other ideas or advice would be appreciated!

Just to be clear, cement is a chemical process which uses water as it catalyst . So cement should not dry for a week, keep it moist. Cement can take months to fully cure but typically you should wait one month before using it. Not sure why you are soaking it with vinegar or salt nor do I understand how that would affect the curing cement.

The term hydraulic means the cement will cure in water so I would just soak it for a regular water for a few weeks. If you still having issue, try sealing the cement with Krylon clear spray paint.

Edit: Sealing the background with epoxy is your best option.

 

[itiwhetu]

I think you have used the wrong product. Start again

 

[Jan Cavalieri]

What a very cool idea, I read that tutorial - I don't think I would have that kind of patience or creativity to create something like that. I agree you need to let the concrete cure for a long time before introducing fish. I wonder if you don't seal the concrete if it will permanently change your water's PH. If so there are Neutralizers on the market that you mix into you water to bring the PH to 7.0 from wherever it is, then depending on the buffering power of your water (KH) the PH may or may not continue to acidify after you add the neutralizer. When I use neutralizer I add it to each bucket of water so I'm not pouring PH 9.4 (my tap water) on the heads of my fish. It drifts down to about 6.5 during the week - that's about as low as it ever gets, and by then it's time to do another water change and bring the PH back to 7. Now if you're planning on working with Cichlids than you want your PH closer to 8.0. There are products called PHup and PHdown you can use - again, how long your water will remain stable depends on it's buffering power - you don't want you PH bouncing around all over the place. I do weekly water changes to keep my PH at 7 (among other things you usually use water changes for) . So keep patient - sounds like you've created something cool - I'm sure you are ready to use it.

 

[Colin_T]

Concrete needs a sealant over it to stop it leaching lime into the water and raising the pH. Pond shops usually sell it or a hardware store should too.

 

[madmark285]

Concrete needs a sealant over it to stop it leaching lime into the water and raising the pH. Pond shops usually sell it or a hardware store should too.

I plan on using White Portland cement which does not contain lime. My mix will be 1 part cement, 3 parts play sand.

Typically mortar is cement, sand and lime, concrete is cement, sand and gravel.

 

[madmark285]

Concrete needs a sealant over it to stop it leaching lime into the water and raising the pH. Pond shops usually sell it or a hardware store should too.

I need to research this, are cement sealers safe for aquariums?

 

[EmilyS]

Thanks for all the suggestions! I'm going to try to address as many of the comments as I can.

If the concrete is raising your pH, there’s nothing you can do to prevent that.

I understand that cement leaches calcium into the water, but many many people have had success with this technique. The person in the tutorial I linked had no pH spikes or drops whatsoever, and I followed his instructions exactly. I can't seem to figure out what I did differently that would cause these different results.

I think you have used the wrong product. Start again

I double checked the concrete I used and it is identical to the one used in the tutorial.

Not sure why you are soaking it with vinegar or salt nor do I understand how that would affect the curing cement.v

I added salt and vinegar because I had seen that suggested in many places as a way to speed up the stabilization process. No one ever seemed to know why it helped, though.

The term hydraulic means the cement will cure in water so I would just soak it for a regular water for a few weeks.

On a similar note, all the tutorials always emphasize the importance of letting the concrete cure, but don't seem to mention why. Even if it needs to be wet to cure, is it possible that it can't cure completely when fully submerged?

there are Neutralizers on the market that you mix into you water to bring the PH to 7.0 from wherever it is

I'm hesitant to use too many pH buffer products because, as you mentioned, they are temporary fixes. Especially considering how fast the background raises the pH, I don't know if I would be able to put enough buffer to keep the pH from spiking. If I can't find another solution, I will experiment with some pH Down that I have.

Sealing the background with epoxy is your best option.

Sealing the background with Epoxy is certainly the best option, but it would be as much work as starting over. Parts of the background are very difficult to reach, so I would have to take the whole thing out before sealing it. If anyone has ever made a background like this, you know that it uses a lot of silicone to both keep fish from going behind the foam and make sure the foam doesn't float. It's already pretty easy to crack the concrete, and removing the background would probably completely destroy it.

Thanks for all your suggestions!

 

[PheonixKingZ]

Thanks for all the suggestions! I'm going to try to address as many of the comments as I can.


I understand that cement leaches calcium into the water, but many many people have had success with this technique. The person in the tutorial I linked had no pH spikes or drops whatsoever, and I followed his instructions exactly. I can't seem to figure out what I did differently that would cause these different results.


I double checked the concrete I used and it is identical to the one used in the tutorial.


I added salt and vinegar because I had seen that suggested in many places as a way to speed up the stabilization process. No one ever seemed to know why it helped, though.


On a similar note, all the tutorials always emphasize the importance of letting the concrete cure, but don't seem to mention why. Even if it needs to be wet to cure, is it possible that it can't cure completely when fully submerged?


I'm hesitant to use too many pH buffer products because, as you mentioned, they are temporary fixes. Especially considering how fast the background raises the pH, I don't know if I would be able to put enough buffer to keep the pH from spiking. If I can't find another solution, I will experiment with some pH Down that I have.


Sealing the background with Epoxy is certainly the best option, but it would be as much work as starting over. Parts of the background are very difficult to reach, so I would have to take the whole thing out before sealing it. If anyone has ever made a background like this, you know that it uses a lot of silicone to both keep fish from going behind the foam and make sure the foam doesn't float. It's already pretty easy to crack the concrete, and removing the background would probably completely destroy it.

Thanks for all your suggestions!

Well, I don’t see how the guy who did the tutorial didn’t get a rise in pH. He probably never actually tested, and if he did, he didn’t tell the people watching.

You could try to seal the whole thing in epoxy, as @madmark285 said. That is pretty much your only option, if you don’t want to completely start over.

 

[madmark285]

On a similar note, all the tutorials always emphasize the importance of letting the concrete cure, but don't seem to mention why. Even if it needs to be wet to cure, is it possible that it can't cure completely when fully submerged?

Yep, it should cure while submerged. I did search about that project, a few others have the same issue. The pH seem to settle around 8.0.

The Drylock product contains lime, as Colin say that may be the issue. I am interested in your issue as I am working on DIY hardscape project using cement. For me, a pH of 8.+ is not a issue since the fish will be African cichlids, Mbunas. I am using plain white Portland Cement, the Drylock product using Portland cement, lime, etc. Not that this helps you but I will test Portland cement effects on the pH.

removing the background would probably completely destroy it.

Understood. Back to the Kyrlon Clear spray paint solution, empty and dry out the tank, tape up the inside of the tank and spray away. This project should have had a warning about pH issue.

Good luck

 

[StevenF]

cements typically contain a variety of ingredients. calcium hydroxide is a major portion of it. When mixed with water the calcium hydroxide will push the PH up. At that high PH it will then react with Silicon in the sand. The final result of the reaction is calcium silicate which is not water soluble and does not have an effect on PH.

Unfortunately not all of the calcium reacts with the sand and may leach out slowly over time. Also there are many vendors of portland cement and sand so not all of them whill have exactly the same ingredeients. Also what is in your tap water will also have an effect on how fast the cement. All of these factors can influence the cure rate and how much an effect it has on PH.

Keeping it submerged will allow any lim to leach out and react but that can take days,months, weeks, or years. It might be possible to accelerate the process by adding sodium silicate to the water (it swather soluble.). it could accelerate the conversion of excess lim to calcium silicate which is not water soluble. I have never done this so I don't know how long that would take.

The easy and quick solution is to do what Colin suggested. Seal it with an epoxy or and acrylic resin. This would react a fysical Parker between it and the cement and water.

 

[madmark285]

cements typically contain a variety of ingredients. calcium hydroxide is a major portion of it.

Just to be clear, Portland Cement is typically made from the following:

Lime or calcium oxide, CaO: from limestone, chalk, shells, shale or calcareous rock
Silica, SiO2: from sand, old bottles, clay or argillaceous rock
Alumina, Al2O3: from bauxite, recycled aluminum, clay
Iron, Fe2O3: from from clay, iron ore, scrap iron and fly ash
Gypsum, CaSO4.2H20: found together with limestone

To make mortar: mix water, Portland Cement, calcium hydroxide (Hydrated Lime) and sand.
To make concrete: mix water, Portland Cement, sand and gravel.

I currently have a block of Portland Cement and sand soaking in water, I post the pH results in a few days.

The question I have for this project, why use the Drylock Hydraulic Cement which has calcium hydroxide (Hydrated Lime) added to it?

 

[Boundava]

Can you paint the background with Drylok? I have made a couple DIY backgrounds for my tanks but omitted the concrete and just painted over the carved/sculpted foam with multiple layers of drylock, finishing with Drylok mixed with acrylic paint or concrete tint for color. Drylok masonry sealer (acrylic version) will not leach anything and is safe after cure time. Meaning it is allowed to fully dry, which I always went from a week after final coat. Here's the bamboo wall I did for my 125 a couple going on 3 years ago.

I decided against concrete for both of my backgrounds due to the leaching. Researched a lot and anything with concrete went through weeks of soaking and draining, (rinse and repeat) before the leaching slowed to a manageable level. Even then it still was an issue for some people. Which is why whenever anyone asks me I always recommend the Drylock acrylic masonry sealer. It's gritty so you have a nice texture but after fully drying it is inert. Plus you can color it or add more sand for even more texture. You can even water it down a bit and get into deeper cracks and crevasses.

 

[madmark285]

Which is why whenever anyone asks me I always recommend the Drylock acrylic masonry sealer. It's gritty so you have a nice texture but after fully drying it is inert. Plus you can color it or add more sand for even more texture. You can even water it down a bit and get into deeper cracks and crevasses.

Thanks for the info. From their website, DRYLOK® Original Masonry Waterproofer is safe for fish ponds once fully cured. Is this what you used? If look more like a paint then sealer.