Questions Re: Ph And Demineralized Water

[rainrad2002]

Hello everyone,

I am new to this forum but not a newbie to fishkeeping.

I have a happy tankful of African Cichlids, and our tap water is naturally hard and as such the ph is always quite alkaline. Obviously this is great for the cichlids. I would like to start adding demineralized water to the tank as well as tap water when doing water changes. How will adding the demin. water affect the ph levels if at all? I am hoping that even though the demin water is exceedingly soft that smaller amounts will not disrupt the natural balance. What do you think?

Cheers,
Lorraine

 

[Bignose]

I would like to start adding demineralized water to the tank as well as tap water when doing water changes.

Ummmm, one question about this.... why?

 

[rainrad2002]

Our water in Alice Springs is EXTREMELY hard, and demineralized or RO water helps tone that down a bit. Limescale is a big problem here with anything that comes into contact with our tap water. The use of demineralized or RO water in aquariums is not unusual in any part of the world. We have just bought our own demineralizer to make water for our house humidifiers, very handy.

 

[Bignose]

OK, but you say yourself that you have a tankful of happy African cichlids. Maybe I should be more specific: so for the fish's sake, why?

As in, if the fish are happy and healthy, why change anything?

 

[rainrad2002]

OK, but you say yourself that you have a tankful of happy African cichlids. Maybe I should be more specific: so for the fish's sake, why?

As in, if the fish are happy and healthy, why change anything?

As I already alluded to in my previous reply, to cut down on the ridiculous amount of limescale buildup in the tank. It is difficult to remove and makes quite a mess. Our water here is like concrete.

 

[Colin_T]

Theoretically R/O water is going to be free of everything and have a PH of 7.0. If you use half R/o water and half mains water then you will drop the hardness by half. The PH is unlikely to change much due to the high mineral content of the mains water.
You will have to make up some water and test it to find out exactly how hard the new water will be and what the PH drops to if at all.

 

[rainrad2002]

Theoretically R/O water is going to be free of everything and have a PH of 7.0. If you use half R/o water and half mains water then you will drop the hardness by half. The PH is unlikely to change much due to the high mineral content of the mains water.
You will have to make up some water and test it to find out exactly how hard the new water will be and what the PH drops to if at all.

Thank you for your help Colin, sounds like it might be doable. Will test it first, and see how it goes.

 

[Bignose]

OK, but you say yourself that you have a tankful of happy African cichlids. Maybe I should be more specific: so for the fish's sake, why?

As in, if the fish are happy and healthy, why change anything?

As I already alluded to in my previous reply, to cut down on the ridiculous amount of limescale buildup in the tank. It is difficult to remove and makes quite a mess. Our water here is like concrete.

OK, that's much more clearer. The real question is whether you want to tinker with the water chemistry, or just find an easier way to clean limescale? Any acid will be good at dissolving & cleaning limescale. Some people have found success with vinegar.

I'm not sure that just diluting the water will significantly change the deposition of limescale. That usually comes from splashing and evaporation of water, and even though there will be somewhat less minerals in the water, what is in the water will still find a way to come out.

Just be careful with changing the hardness of the water too much too fast. While changes in pH and changes in temperature have received a bad reputation, there is a significant amount of evidence that changes in hardness are actually probably the most stressful on fish. I've collected a lot of the information about hardness changes in my post in this older thread: http/www.fishforums.net/content/forum/20...-Home-Aquarium/

 

[ac700wildcat]

I'd just like to add to the statement that RO water has a ph of 7.0. This is incorrect unless I'm getting sold water that isn't actually RO. The RO water that I have been purchasing tests to have a ph of 6.0, the lowest that my API liquid test kit tests for. Also, several different different distilled waters test at 6.0 as well. I will have RO here in my home in a week or so and can't post results of that as well.

Matt

 

[Dave Spencer]

I'd just like to add to the statement that RO water has a ph of 7.0. This is incorrect unless I'm getting sold water that isn't actually RO. The RO water that I have been purchasing tests to have a ph of 6.0, the lowest that my API liquid test kit tests for. Also, several different different distilled waters test at 6.0 as well. I will have RO here in my home in a week or so and can't post results of that as well.

Matt

Pure RO water will have a pH of 7. Yours is lower because CO2 from the atmosphere has dissolved in to it to reduce the pH.

 

[Bignose]

I'd just like to add to the statement that RO water has a ph of 7.0. This is incorrect unless I'm getting sold water that isn't actually RO. The RO water that I have been purchasing tests to have a ph of 6.0, the lowest that my API liquid test kit tests for. Also, several different different distilled waters test at 6.0 as well. I will have RO here in my home in a week or so and can't post results of that as well.

Matt

Exactly what Dave said. The pH of 7.0 for pure water has been confirmed time and time and time again. Unless you want to be completely technical about it in which I think that 7 is only accurate to 2 decimal places. I think at 25 degrees C, the pH of pure water is actually 6.998 +- 0.001. Though, for all but the most sensitive of applications, saying 7 is going to be accurate enough.

When the water is pure, it is very, very quick to take up anything that will dissolve in it, like CO2. Or any kind of residue in the container. Or almost anything else. That's why it is often very hard to actually measure the pH of a pure substance.

 

[ac700wildcat]

Thanks for correcting me. How fast will it absorb CO2? I've tested a jug right after opening it and get 6.0. Maybe its exposed before even going into the jug and getting sealed.

 

[Bignose]

Thanks for correcting me. How fast will it absorb CO2? I've tested a jug right after opening it and get 6.0. Maybe its exposed before even going into the jug and getting sealed.

If it exposed to air anywhere, it will take up CO2 from the air. And when it is so empty, it will take up anything pretty fast.

 

[OldMan47]

Another common misconcception is that RO water is pure water. An RO will only remove between 90 and 95% of the TDS in the water. This is based on the published benefits of RO by the people who sell RO units. In my own case I read 230 ppm in my tap water and 20 ppm in my RO. The remaining dissolved solids are not inert and are not necessarily neutral in pH. The TDS in RO water is low enough that anything you add to it will become the dominant dissolved solids but before you add anything there is no saying what it will be like. It depends on the water it was made from and what compounds the RO was trying to remove.

Edit: spelling

 

[Dave Spencer]

Another common misconcception is that RO water is pure water. An RO will only remove between 90 and 95% of the TDS in the water.

I think you are talking about domestic RO units. Where I work, our RO units remove 99% of the TDS. The RO units are only one of four steps in demineralisation, but we have always tended to call the final product RO, although the correct term is demineralised water, but even this isn`t pure water.

The final product has a purity of 0.02mS/cm on a good day, which is only bettered by the microchip and nuclear power industries, as far as I am aware. Our pH measures 7 at the outlet of the water treatment plant.

Dave.