Replacing water

[dthom2701]

Does pool water need to be replaced periodically?

[Is it summer yet?]

I have only one year of pool experience but here is what I know.
I live in Minnesota.
I drained my 18 X 36 in ground down 1.5 feet for closing last fall.
With snow melt it has come back up about 10" to 12".
Snow and Rain are naturaly soft water.
I asked my pool company your exact question and they said no.

The reason is if you refill the pool you will need a lot of different chemicals to restablize everything.
I am on a well with a bit of Iron so if I am not careful when I do have to add water all the preaty white plastic turns orange. The pool store has chemicals to add when refilling and chemicals to remove the stains after the fact but it is better to add the preventitive then to fix it afterward.

I guess I have come a long way to say this.

As long as you keep the chemicals balanced, shock as needed, keep your pool and filter clean, you should not have to replace the water.

First response. Now I find out if someone thinks I am an IDIOT. I would say idiot, no. Newbe to a pool yes.
You can fix Ignorance but stupid can't be fixed.

[chem geek]

You should be replacing at least a portion of your pool water regularly, at least annually. If you have summer or winter rains that can overflow the pool, then you get such dilution "for free". If you have a sand filter that you backwash weekly (or so) then you are getting dilution, though are paying for the fill water that replaces it.

In a non-SWG pool, you are building up salt over time since chlorine gets converted to chloride (salt) as it gets broken down. With any source of chlorine, for every 10 ppm Free Chlorine (FC) this gets converted to 8 ppm salt. With bleach and chlorinating liquid, these add an extra 8 ppm salt upon initial addition.

In a saltwater chlorine generator (SWG) pool, the salt level does not increase since the chlorine is generated from the salt (chloride) itself. Nevertheless, there is a buildup of other dissolved solids so it's still a good idea to regularly dilute the water.

In commercial/public pools, the general rule is a water replacement of 7 gallons per bather per day (or per use).

Richard

[Is it summer yet?]

I stand corrected.
Thank you,

[Bjorn]

It is not necessary to replace your water in the pool as long as you care to manage your water balanced properly. You'll probably during the season need to add up with water due to evaporation. In Denmark, we have much rain and therefore we start the pool without add up with water. But during the season we need to add up with water. Good control of your water balance is god!

[chem geek]

Bjorn,

We aren't talking about a full replacement of the water, but if you do not have ANY water replacement, then chemicals WILL build up over time, though it can take several years before it becomes an issue. ALL sources of chlorine will increase salt levels (except SWG that I talk about later). If one uses chlorinating liquid or bleach or even lithium hypochlorite (expensive!) in order to avoid any buildup of Cyanuric Acid (CYA) or Calcium Hardness (CH), then for every 10 ppm Free Chlorine (FC), the salt level will increase by 16 ppm (8 ppm upon addition and another 8 ppm when the chlorine gets used up and converted to chloride).

Even at a low 1 ppm FC per day chlorine usage, after 21 months this is 1000 ppm salt. If the chlorine usage is a more typical 2 ppm FC per day, then that's 1000 ppm salt increase in around 12 months of pool use (around 2 years if the season is 6 months long). Not a big problem since saltwater chlorine generator (SWG) pools have 3000 ppm, but after a few years you will have high salt levels unless there is SOME dilution of the water. If one has an oversized cartridge filter and doesn't have any rain overflow, then the amount of dilution from splash-out is minimal. Those with sand filters regularly backwashed or with rain overflow will have some dilution.

Also, there are some organics that do not oxidize fully by chlorine and are not completely soluble (so can get saturated at some point) and these can also build up over time. One could potentially use enzymes to clear this, but if one does SOME water dilution then one takes care of the increasing salt levels at the same time as the increasing organics.

As I mentioned in the previous post, if you have an SWG pool, then you don't get any increase in salt levels since the chlorine is created from the salt and then gets converted back to salt as it gets used up. Nevertheless, there still is a buildup of non-chlorine-oxidized organics, but this can take years before this becomes an issue so there is less need for dilution in an SWG pool.

Richard

[Bjorn]

Hi Richard,
I see your point. It has never been necessary to replace the water in outdoor pools i Scandinavia, because we normally use sand filter and therefore have some dilution by frequenty backwash. Here in Denmark we have to reduce the water level (1 / 4) before the winter time starts (water freezes). Howeverover, there so much rain and snow in wintertime, so the pool is almost filled up with water when the frost stops.

[chem geek]

Backwashing and partial drain and rain refill count as some water replacement.