Question about tap/ro water pH concerning aragocrete/oystercrete rock

[lordofthereef]

I was wondering what all of your tap water reads as far as pH os concerned. As you may (or may not) know, I made a bunch of aragocrete dry rock. My pH test kit reads from 7.4 to 8.8. Initially I was using RO water, which reads 7.4 going in with the rock and 8.8 coming out after 24 hours. I decided that it may be wasteful to use so much RO every day (would be about 45 gallons I estimate) so I went with tap water tonight. I realized that my tap water is reading 8.8 before it even hits the rock, so basically my tap water is 8.8+ I wasn't necessarily expecting the tap water to be identical to the RO water, but I was shocked to see such a high ph and that water. Any idea of this is going to effect my end goal of leaching all the "bad stuff" out of the rock? I was sort of banking on being able to do a water test every night once the water has been in with the rocks for 24 hours in order to get some sort of visual as to when the pH finally starts dropping enough.

I made this same listing (different name) in the reef forum too in hopes that more eyes see it, who may not frequent here.

[Randy Holmes-Farley]

My tap water is in the 9's. Many localities raise it intentionally to reduce copper and lead release from old pipes. :)

You can add a bit of muriatic acid or vinegar to it to drop it. It doesn't take much. :)

[lordofthereef]

Thanks Randy. Since you know what I am doing here, would you add the vinegar at this point? Would you stick with tap water or would you go with the RO?

[Randy Holmes-Farley]

I'd add some acid to at least pH 6-7. :)

[lordofthereef]

Alright. Thanks Randy :)

[Randy Holmes-Farley]

:thumbsup:

Good luck. :)

[lordofthereef]

Came up with a few more for you Randy!

Should I be concerned about the rock absorbing any of the potentially bad stuff from the tap water? I am getting mixed statements about still using tap, namely regarding phospahtes.

I added the vinegar and got the PH down to at least 7 (I have no way to test if it got below that currently). By the evening it was back up over 9. Should I add more vinegar at this point or would you say I should swap the water out now? I am just trying to get myself on a fairly regular regimen here.

As always, thanks for all you do for the community!

[bertoni]

Well, the quality of tapwater is variable. I'd stick with RO/DI, perhaps mostly out of an excess of caution.

If the pH is back up, adding more acid is fine.

[lordofthereef]

Ok. I am fine adding more acid, but to what end? At what point should I consider just dumping the water and refilling with fresh? The pH goes back up in a matter of hours, just as reference.

[bertoni]

Well, a mineral acid will destroy the alkalinity permanently, and thus remove the need for changing the water. The vinegar will be consumed over time, releasing the alkalinity, so you might need to change the water every few days or so. Both approaches will save water and work. :)

[lordofthereef]

The vinegar seems to work well, but after a few hours the pH is right back up. A good thing as far as leaching out the rock is concerned, a bad thing since the amount of rock is taking 1/2 gallon of the vinegar a day. My rocks are about 25-40 pounds a piece, extremely porous. I am wondering if I should omit the vinegar at this point. Trying to keep this venture as cheap as possible, which was part of the decision to go with DIY rock.

[bertoni]

Using more water might be cheaper. :) Muriatic acid is a dangerous to handle, but it's likely to be cheaper than vinegar by a large margin.

[lordofthereef]

Where would I get the stuff?

EDIT: a quick online search showed an average of about $5 per gallon? That's more than I paid for the vinegar by quite a bit LOL. (unless I would need to perhaps use much less of it for the same effect_

[stormrider27]

lord, how long did you allow your rock to cure before placing them in water? I ask because I am about two weeks out from starting to make my own DIY rock.

Thanks!

[bertoni]

Muriatic acid is far more effective per unit volume than vinegar. :) Lot of hardware stores and pool supply shops carry it. Be careful handling it!

[lordofthereef]

Any idea how much more? Twice? Three times? Ten? LOL sorry for all the questions, it's just the local 99 cent store has gallons of offbrand white vinegar for a buck :)

[bertoni]

More like 10 to 100, I think. :) pH 2 or so, versus ph -1 to zero or so.

[lordofthereef]

Guess that really might be worth it. I'll have to try it. Can I just pour in a "splash" with the water to limit the amount of contact/handling I need to do with it?

[bertoni]

I would try to dose a somewhat consistent amount, and avoid any splashing. :) Pouring a bit in might be fine. I'm not sure how big your container will be. Be careful, in any case.

[lordofthereef]

The container is a 70g stock tank about 85% full. I have around 200lbs of rock in there. I estimate somewhere around 40 gallons of water give or take. By splash I just meant "small amount" or something synonymous. Was trying to avoid exact measurement any just eyeball it, if at all possible.

[Randy Holmes-Farley]

To acid content of ordinary vinegar is about 0.83 moles/L.

The acid content of muriatic acid from a hardware store is about 11.6 M, or 14 times as strong.

The pH is even more dramatically different, because some of the acid in the vinegar is present in the unionized state: CH3CO2H, rather than as CH3CO2- and H+, while the HCl is fully ionized to H+ and Cl-.

pH plays a role in dissolving CaCO3 deposits on pumps and such, but not for your application where you will not be wanting to drive the pH lower than 6 anyway, so all the acetic acid in vinegar will be fully ionized. :)

[lordofthereef]

So then would the muriatic acid be a bad idea? I wasn't so much attampting to drop the pH lower than 6 as just use less product as I have been using lots of vinegar currently. My thought was I could just stretch a gallon of muriatic acid MUCH longer than a gallon of vinegar? Is my thought process wrong on that?

[Randy Holmes-Farley]

No, it is a fine idea. You would add 14 times less than the vinegar you are now adding. It is definitely not 14x as expensive if you buy it in 1 gallon jugs from a hardware store.

[lordofthereef]

Cool. Should the molarity of the acid be available to me somewhere on the bottle? I figure I can compare the molartiry of the muriatic acid I buy to that of the vinegar and "dose" the tub accordingly? Or would it just be a safe bet to literally do 1/14 the amount of vinegar I was currently using.

Another slightly off topic question. Can I use this stuff (heavily diluted of course) to clean things like pumps and the like? Something like ten parts water to one parts muriatic acid?

[Randy Holmes-Farley]

Should the molarity of the acid be available to me somewhere on the bottle?

No, I calcualted those. Wikipedia converts it for muriatic acid from the weight percent (which will be on the bottle; about 36%):

http://en.wikipedia.org/wiki/Muriatic_acid

yes, 1 part acid to 10 parts water is great for cleaning CaCO3 deposits from plastic and glass.

[Randy Holmes-Farley]

My vinegar calculation is:

5% acetic acid (typical vinegar) = 50 g/L.

mw of acetic acid is 60 grams per mole

So 50/60 = 0.83 M

[lordofthereef]

Well, guess I will never waste money on vinegar again. Thanks for all the help!

[lordofthereef]

lord, how long did you allow your rock to cure before placing them in water? I ask because I am about two weeks out from starting to make my own DIY rock.

Thanks!

I completely missed this question. I do apologize. better late than never I guess...

I don't know if I have the right terminology, but the rock dried for 2-7 days. After a 24 hour period of being out of the sand mold it was completely dry. I only had enough space to do 1-2 rocks at a time and I worked on them for about a week.

[stormrider27]

I completely missed this question. I do apologize. better late than never I guess...

I don't know if I have the right terminology, but the rock dried for 2-7 days. After a 24 hour period of being out of the sand mold it was completely dry. I only had enough space to do 1-2 rocks at a time and I worked on them for about a week.

No problem, thank you for taking the time to go back to read then answer my question. The reason I asked is that I am in the first stage of making my DIY rock and have been trading PMs with Mr. Wilson. Mr. Wilson makes concrete reef structures for public aquariums and recommends allowing the agrocrete 28 days to cure in a warm moist environment before soaking. He claims that by doing so it reduces the 'kuring" (aka soaking to reduce high PH levels) significantly. I am going to follow Mr. Wilson's method and will report my results.

[lordofthereef]

Well if he makes structures for public aquariums he probably know more than I do! LOL. I hadn't come across anyone saying that it needed anywhere near that long so I just dropped mine in. Hopefully it works out for me! :) Best of luck to you too!

[lordofthereef]

http://www.cement.org/basics/concretebasics_faqs.asp

Thought I would link you to this. It is not aragocrete information or anything, but it is info on curing concrete itself.

From the article:
"Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete's temperature stays within a suitable range. During the curing period-from five to seven days after placement for conventional concrete-the concrete surface needs to be kept moist to permit the hydration process. new concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture."

[stormrider27]

That mirrors Mr. Wilson's advice. He told me to keep the concrete damp but not immersed for 28 days to allow the concrete to fully cure then soak.

From the Ultimate DIY rock Thread: "let them air dry for a month. The hydration process that cement goes through allows the calcium to become part of the rock. Adding the rock to water before it cures fully will release calcium and other caustic constituents into your water. The rock will also be weakened by this process." -Mr. Wilson

[lordofthereef]

Hmmm, I was under the impression that all that was supposed to leach out of the rock into the water. Oh well, not too worried as I am pretty sure others have done it this way as well. I'll report either here or make a new thread once things are leaching.