High PH

[BrianR]

I have had a new garden pond built. They used concrete, not a plastic liner, and I was assured that it was finished off using the correct recommended "paint".

I fill it with tap water (PH 7.4), but a day or so later the PH is off the scale (at least 8.6). Since discovering this I have emptied it and filled it numerous times but it does not seem to be improving.

I obviously cannot put any fish in it. Frog spawn appeared a few weeks ago, but the tadpoles all seem to have died.

What can I do ?

BrianR

 

[MoonShadows]

Sorry to hear about this problem.

First, I would contact the company and ask them exactly what "paint" they used. There are special epoxy paints made for this situation that will keep the lime from leeching into the water. Research what they tell you, and if you find out they used the wrong "paint", tell them you want it sealed properly. Hope you didn't pay the whole bill, yet. Do not try to play with the ph with chemicals. It won't work. Bottom line, either the company or you are going to have to drain the pond and treat the concrete properly.

 

[sissy]

ph swings are normal in a new pond .

 

[Meyer Jordan]

I have had a new garden pond built. They used concrete, not a plastic liner, and I was assured that it was finished off using the correct recommended "paint".

I fill it with tap water (PH 7.4), but a day or so later the PH is off the scale (at least 8.6). Since discovering this I have emptied it and filled it numerous times but it does not seem to be improving.

I obviously cannot put any fish in it. Frog spawn appeared a few weeks ago, but the tadpoles all seem to have died.

What can I do ?

BrianR

How long was the concrete allowed to cure before the coating was applied?

 

[Waterbug]

I fill it with tap water (PH 7.4), but a day or so later the PH is off the scale (at least 8.6). Since discovering this I have emptied it and filled it numerous times but it does not seem to be improving.

I obviously cannot put any fish in it. Frog spawn appeared a few weeks ago, but the tadpoles all seem to have died.

What can I do ?

You can put fish in it. Who told you you couldn't? Lots of ponds have high pH. Some of the highest end Koi ponds run at around 8.4 pH. I run mine a bit above 9.

Also, pH can be tricky to measure. It fluctuates throughout the day for example. Here's a good video, just skip the numbers, that explains pH very well.

We live in a digital world. We see 8.4 and assume it must be accurate or there wouldn't be a decimal point. There's more to it. Shaking the water before and during the test can change the pH. It's a way more tricky test than most people think.

A much easier way to deal with this is to throw out the pH test and use KH instead. Keep KH up and you know pH will be pretty stable and that's what we should care about in fish ponds for the most part. Keeping KH up does drive pH high, 8.4 and above but that's what many experienced pond owners call good.

 

[Waterbug]

The concrete is not responsible for the high pH. CO2 seals concrete against meaningful effects on pH at least in the pH range of ponds.

 

[Meyer Jordan]

The concrete is not responsible for the high pH. CO2 seals concrete against meaningful effects on pH at least in the pH range of ponds.

Do you have a source for that statement? Concrete that is not properly cured will leach and elevate pH.

 

[BrianR]

How long was the concrete allowed to cure before the coating was applied?

How long was the concrete allowed to cure before the coating was applied?

 

[BrianR]

Thank you for your reply.
I'm not quite sure what "cure" means, but it was allowed to dry out for about a day.

 

[BrianR]

Thank you for your reply.
I'm not quite sure what "cure" means, but it was allowed to dry out for about a day.

 

[Meyer Jordan]

It typically takes concrete about 30 cays to fully cure (set). It should be allowed to cure for at least 7 days before any sealant or coating is applied.

 

[BrianR]

Thank you - so the concrete was not allowed anywhere near long enough to cure.
How do I get myself out of this mess?

 

[Mucky_Waters]

Do you have a source for that statement? Concrete that is not properly cured will leach and elevate pH.

LOL He posted a link to his source. >>> http://www.waterbugdesign.com/pond/myths/cement.html <<<

The surface of fresh concrete does generally have high PH, but you can coat it with certain types of paints and products before the concrete "cures" (reaches it's minimum required compressive strength). which could be anything from 24 hours to several years depending on the specific mix. The 28 or 30 days is really just an arbitrary time period chosen by authorities as the standard specimen age to establish consistency for testing procedures throughout the industry and applies more to the minimum required compressive strength.
The problem with coating fresh concrete arises more if the concrete hasn't fully dried or the product you are using has a much different PH (eg;lower PH) than the fresh concrete and there is a adverse chemical reaction (acid vs alkaline) between the applied product and the concrete causing poor bonding. As long as the product (eg; paint) has similar PH as the raw concrete and the concrete has thoroughly dried you should get satisfactory bonding. Of course another factor to consider is the temperature and humidity at the time of application. Obviously too hot or cold temps could also adversely effect how well the product bonds to the concrete.

As far as your pond water having a PH of 8.6, as Waterbug points out that isn't bad, it's about the same average PH level as my last pond stayed and my fish, frogs and turtles thrived. I would still drain the water to rinse the pond out at least once. You may find the average PH level start to drop as you get a growth of bio-film on the concrete surface in your pond, but if you find the PH level fluctuates radically you might find your KH level is too low. Generally, in a pond a PH level 7.5 to 8 is ideal, a steady PH of 8.6 is still fine and is much better than anything below 7.

 

[Waterbug]

Do you have a source for that statement? Concrete that is not properly cured will leach and elevate pH.

You added the "not properly cured", not me. But I'll play. Not sure what you consider "properly cured" to be but carbonation happens pretty fast, a day or two.

I find Google works pretty well for finding stuff. Try "Carbonation of concrete" You a very long list saying the surface pH of concrete with carbonation is ~6 to ~8 pH. Which is below what most ponds are so the carbonation stays on the surface. This is also why concrete is such a poor pH buffer in the pond. The water pH has to drop very low before the concrete will bring it back up and it is very slow to do so.

There are a lot of studies on concrete sewage pipe and pH effects.

In construction we perform pH tests on concrete surface before applying epoxy. The surface is ground down to remove the carbonation. When pH is 9-9.5 we know we've reached "fresh" concrete. So even then the pH is pretty low. But of course concrete doesn't stay fresh for long.

If you prefer pond specific...There's a guy named Rich on Koipen who describes the process very well and in great detail. This is back awhile so you might have to try their archives.

There's this brilliant guy's experiment. Very easy experiment to reproduce.

Then there just good old common sense. Consider how long concrete ponds last or even better, concrete cisterns. Well more than 100 years. Given the amount of acid ponds produce, and given the rain water collected in cisterns is < 5 pH it is not possible for the concrete to be having much effect on the pH of the water. Because if it did the concrete would dissolve in a rather short time...less than 100 years for sure.

 

[Meyer Jordan]

https://www.researchgate.net/public...lkali_from_Concrete_in_Contact_with_Waterways

http://www.resene.co.nz/pdf/PreparingConcreteFloors.pdf

http://www.concreteconstruction.net/how-to/how-long-a-wait-to-paint_o

http://homeguides.sfgate.com/long-need-wait-before-putting-epoxy-paint-new-concrete-91844.html