Reduction of CH

[iwannapool]

I thought I read somewhere you could lower CH by slowly adding trisodium phosphate. I believe this is the common cleaning product, TSP.

[fcfrey]

My old brain has lost a lot of what I learned in chemistry class in the 60s so I did a search on Trisodium Phosphate. Here is an extract from the Wikipedia listing:

"Similar chemicals were once common in laundry and dishwashing detergents, but the phosphate, being a fertilizer, would cause algal blooms in the bodies of water that the drains led to. In the early 1970s the use of phosphate-containing products was limited. Now products sold as TSP Substitute, containing 80–90% sodium carbonate, are promoted as a direct substitute."

Notice what it says about ALGAE---- Richard may want to weigh in, but I would not intentionally put phosphates in my pool.

[chem geek]

If you maintain proper chlorine levels, then phosphates will not cause an algae bloom. Basically, you can keep algae from growing in any number of ways:

1) Keep out all light. Algae needs at least some sun to grow (though not too much or the UV from sunlight ends up doing too much damage). Unless you are indoors and swim in the dark , this is not an option.

2) Take away at least one critical nutrient. This includes carbon from carbonates (can't take that away -- need it for pH buffer and calcium carbonate saturation), nitrogen from nitrates (hard to eliminate since it's in many bather wastes), phosphorous from phosphates. So really the only one you can realistically eliminate is phosphates (with a phosphate remover -- usually expensive), but it can always get blown in from farm (or your garden) fertilizer, etc.

3) Use an algaecide (PolyQuat 60) to prevent algae from growing and add it weekly.

4) Maintain proper disinfecting chlorine levels (enough chlorine for the pool's CYA level).

Option #4 is generally the easiest thing to do and is what is promoted on this pool forum. Since you have to have chlorine anyway for disinfection, you might as well just maintain its level to prevent algae growth and not have to add anything else.

Richard

[iwannapool]

So how can one reduce CH besides draining water off and replacing with water that contains no/little calcium?

[chem geek]

Other than drain/refill with low CH water, the other way to reduce CH is putting the water through a water softener (ion exchange resin or equivalent). This is usually impractical for a full volume of pool water, but is useful for fill water once a pool is already filled.

However, even high CH should not really be a problem because one can significantly lower the TA level to compensate and keep the pH at 7.5 or below. This will prevent scaling and the lower TA level will help reduce the tendency of the pH to rise. The only downside to the low TA would be if you used an acidic source of chlorine such as Trichlor since the pH would get lowered faster in that case, but this just means more frequent monitoring of pH. If you use chlorinating liquid or bleach, then there is no problem as the pH is usually stable or rising, not dropping.

The "standard recommended" values for TA and CH are based on handling a variety of chlorine sources and on trying to give a relatively narrow set of ranges for the parameters. However, water with a TA of 50, CYA of 30, pH of 7.5, and CH of 700 is perfectly balanced (saturated with calcium carbonate). So unless the CH is extraordinarily high, say 1500, keeping a lower TA is usually all that is needed.

Richard

[njpool]

Other than drain/refill with low CH water, the other way to reduce CH is putting the water through a water softener (ion exchange resin or equivalent). This is usually impractical for a full volume of pool water, but is useful for fill water once a pool is already filled.

Why is it "usually impractical"? Is it because the softener would have to be constantly recharged with brine?

I ask because my parents operate a pool at their beach resort in the Philippines and have issues with cloudiness. The pool man needs to constantly add pH down/acid to stop it from clouding up. I figure it is due to the well water they use, which is rather hard. I believe as the pH goes up, the calcium would 'precipitate' out. I suggested they put in some kind of water softener to reduce the hardness, but not sure how to configure it. I read that you could use zeolite as the exchange medium. Currently, they have a DE filter. If you added a sand filter to the mix and use zeolite instead of normal sand, I would think the only other issue is how to plumb the system for the recharge cell.

[waterbear]

I thought I read somewhere you could lower CH by slowly adding trisodium phosphate. I believe this is the common cleaning product, TSP.

TSP (the real stuff, not the substitue) has been used to lower calcium levels in pool in the past but is not commomly used anymore since the result of it is usually an algae bloom because the pool is now filled with orthophosphates! We are talking about REALLY HIGH phosphate levels! Back in the day I believe they hit the pools with copper afterward to keep the algae at bay.