Me in the Deep End.

[Vince-1961]

OMG, I am wading into the Deep End. I'm probably going to drown but here goes.......

Adding Cal-hypo is adding Ca(ClO)2, which reacts with the water H2O to get hypochlorous acid (HClO) which means there is leftover one calcium, one hydrogen and two oxygens. I haven't had chemistry since high school, but wouldn't that be calcium hydroxide or CaHO2? I don't profess to understand how sunlight breaks up HClO, but would not the end result of that process be calcium chloride, water and an extra oxygen which just bubbles out the surface? CaCl2 + H2O + O? Is this not the same calcium chloride that is "Calcium Hardness", which is required for concrete and plaster pools?

I am aware the cal-hypo increases pH and that it's the increase in pH which is what makes the water cloudy.

So, why don't we just "chlorinate" concrete and plaster pools with Cal-hypo all the time and use muriatic acid to keep the pH down?

Is the calcium hydroxide one of the hydroxides that balances Total Alkalinity?

Or perhaps......

I should just go ahead and inhale a lungful of water now and put me out of my deep end misery!

 

[JoyfulNoise]

The calcium ion doesn't really matter to the overall reaction, we call them "spectator ions" because you can basically ignore them since the main part of the reaction that you care about is the hypochlorite converting into hypochlorous acid (In reality, you care more about calcium ions because they contribute to the CH whereas sodium ions do not matter as they and their compounds are highly soluble in water). But what happens with cal hypo is that the two hypochlorites (OCl-) you add create two hydroxides (OH-) which is why the pH increases. Cal-hypo also brings along with it from it's manufacturing process some calcium carbonate and some calcium hydroxide which itself is a very strong base. The hypochlorite does eventually degrade into chloride ions (Cl-) but it doesn't matter what the counter ion is, calcium or sodium.

Think of it like this - when you dissolve sodium chloride into water it breaks up in a sodium ion (Na+) and a chloride ion (Cl-). Those ions become completely hydrated, that is, they become surrounded by water molecules (for many reasons both chemical and electrostatic). That's called creating a "aqua-complexed ion". Once that happens, as long as charge neutrality is maintain (which it must be), then it no longer matters where the ion came from...it acts totally of it own accord.

If you strictly used cal-hypo to chlorinate a plaster pool, the pH would be driven so high (especially near the surface of the plaster) that you would scale calcium all over the pool surface making it blotchy and rough. Calcium carbonate is hundreds of times less soluble than other carbonates and so water can not hold much calcium before it reacts with the carbonate alkalinity (bicarbonate mostly) to form calcium carbonate. You would then need a lot of acid to attempt to keep the pH under control which would just be too costly and problematic.

Cal-hypo chlorination works best in vinyl pools where the swim seasons are short and there's a lot of fresh water exchange from backwashing and winterization. In that case, if managed properly, a vinyl pool can be run quite easily on a alternating schedule of bleach and cal-hypo with very few side effects. The nice aspect of cal-hypo is that is six times less weight and volume for the same amount of available chlorine in liquid bleach.

 

[Leebo]

The key reason why shy away from it is that it also adds calcium to the water. In some parts of the country the CH levels will VERY quickly increase and calcium scaling will occur. If however a user closely watched their CH level one could maintain for awhile using cal-hypo, but after awhile they would likely need to switch back to liquid.

 

[Vince-1961]

Ions? Hmm, I vaguely remember them having something to do with electrons......very vaguely.