hard water to softer water

[4=grand]

i have a pair of pelv taeniatus moliwe.in 30 gal ph is 8.0 need to drop it down more softer.ive read rain water or ro water well do.i have drift wood javamoss in tank .what would be best optionni read that ph matters for breeding and male female ratio on fry.

 

[tjudy]

Central Indiana (I lived there for five years and ran a store in Bloomington) has very hard water with a lot of carbonate hardness due to the limestone-rich rock that the ground water comes from. There is no way to reduce that amount of hardness by adding anything to the tank. R/O is the way to go. Get the pH as close to 7 as possible. Moliwe will spawn in harder water, but there is a pH-dependent sex ratio issue to contend with.

 

[Tedstank]

Ted is absolutely correct, and remember it is easier to raise the Ph with tap water than to lower it with RO water. I use a mix of 25% tap to my ro water (however much I'm mixing) but you will need to figure it out with your tap water.

 

[Mike Wise]

Also note that pH is not directly correlated to water hardness. It is possible to have acidic hard water and alkaline soft water.

 

[dw1305]

Hi all,
Mike wrote

Also note that pH is not directly correlated to water hardness. It is possible to have acidic hard water and alkaline soft water.

Very true, this is why I prefer to measure dKH and conductivity. Without getting too technical, pH
is a bit of a funny measurement. Because acidity/alkalinity is difficult to calculate, or compare (without using titremetric methods) the pH scale was developed which acts as a proxy, by expressing acidity/alkalinity in terms of the equivalent activity of H+ ions (also called "protons", and actually in the form of hydronium ions H3O+). The same applies to alkalinity in the pH scale (proxy of the OH- ions) and probably the easiest way to visualise this is that:

acids are H+ donors
and alkalis are H+ acceptors.

If you add peat or bog wood to hard water, the humic acid (from the wood/peat) binds the positively charged calcium (Ca2+) and/or magnesium (Mg2+) etc ions, and exchanges them for positively charged hydrogen ions (H+), making it a H+ donor and ......decreasing the pH.

However there is a problem with this, and that is that in hard, carbonate rich water both the amount of Ca2+ ions and HCO3- ions will be huge, (it is strongly "buffered") and the amount of H+ ions you would need to provide is correspondingly huge, realistically it means that you can't soften hard water with peat or bog wood and the pH will remain unchanged at pH7.8 ish.

In fact you can't usefully produce soft water by adding any compounds. If we add a stronger acid we can reduce the pH, but this will cause the all ready high TDS/Conductivity value to rise even higher. You can substitute any salt and acid in the graph (below).

If we exchange the multivalent (Ca2+ etc.) ions for monovalent (sodium Na+ etc.) ions, we can soften the water like a domestic water softener does, but the conductivity will remain high because we have just exchanged a metal that contributes to dGH for one that doesn't. If we add a "pH down" buffer we are adding extra salts that will raise the conductivity etc.

The difference is that rain-water (naturally distilled), or R.O. (H2O molecules forced through a semi-permeable membrane under pressure) are pure H2O and have no solutes, and therefore no conductivity, no dGH and no dKH. In pure H2O pH is a meaningless measurement as any addition of H+ ions (or loss of H+ ions), however small, will cause the pH to decline to very low levels (H+ addition) or climb to very high levels (H+ removal). These swings in pH can be observed even in my to some degree buffered water where the pH will change from below pH7 before lights on when the water is CO2 rich, to well above pH7 when the plants are actively photosynthesising, CO2 is low and O2 levels are high.

If we conclude the peculiarities of pH make it of limited use as a measure on its own in soft water, the easiest measurement to take is conductivity, as this is a measurement of all the ions in solution. Personally I'm pretty sure that low conductivity water is what is important in keeping soft water fishes.

Because I have carbonate rich tap water (18dKH), that is of otherwise good quality, I know I can mix tap and rain-water to give aquarium water with a dKH of about 4 at about 150 microS conductivity (93 ppm TDS). I then just need to change the proportion of tap and rain-water to produce harder (more tap) or softer (more rain) water.

cheers Darrel

 

[Stickzula]

WOW very informative! How does one come about such knowledge?

 

[dw1305]

Hi all,

How does one come about such knowledge?

From Wikipedia. I look after a lab at a smaller UK university where we have done a lot of work on the biological reclamation of landfill leachate. I'm not a chemist (I'm a botanist and later on worked on alternative growing media (to peat)), but I've worked with environmental chemists, ecologists etc.

I never really understood buffering or pH properly ("acid and conjugated base", "dissassociation constants", but what do they mean?) until a colleague explained it in terms I could understand, and then the penny dropped. Once I actually understod what was happening in buffering, I could then apply that principle to other situations etc.

cheers Darrel