Refill Experiment

[mas985]

Every year I need to replace at least half of the pool water due to high calcium but this year, instead of a traditional drain and refill, I tried something different.

I had read of people doing an in place refill using plastic to separate the new water from the old water. So I thought to myself that perhaps the water would stay separated on it's own without the plastic as long as the water was introduced at one end of the pool and removed from the other plus remained fairly still during the process. There would probably be some migration but over all not that much so I decided to try it this year.

I plugged both skimmers and kept the deep end main drain as the only water source. I then used the hose to introduce water at the shallow end via the plugged skimmer backwards. Since I went to a two speed pump this year, I used low speed with some extra head loss, basically redirected all of the water through a long hose, to reduce the flow rate to be the same as the replace rate of the other hose (~7 GPM). I let this run for about 24 hours. The pool level seemed to stay fairly constant and still.

Afterwards, I tested the calcium level and sure enough it went down to the expected value. I think what may of helped as well is that I have a salt water pool and the salt water should have been both heavier and colder than the new water and stayed closer to the main drains. I was interested if anyone else had tried this method before and if they were successful. Obviously this wouldn't work for a 100% replacement but I figure I could probably replace most of the water this way.

Also, this could be useful for those with vinyl pools or worry about ground water raising the pool during a water replacement.

[Update 2017] - My last refill, I was able to replace close to 90% of the water without it mixing.

Reference:

Replacing water in-place process depends on several factors.

Pool Water TDS (PWTDS)
Pool Water Temperature (PWT)

Fill Water TDS (FWTDS)
Fill Water Temperature (FWT)

DeltaT = (PWT - PWTDS/165) - (FWT - FWTDS/165)

If DeltaT is positive, then you want to fill at the lowest point and extract at the surface and at the greatest distance from the lowest point.

If DeltaT is negative, then you want to extract at the lowest point and fill at the surface and at the greatest distance from the lowest point. <-Preferred as it is easier to do with a drain pump and you can fill inside one of the skimmers.

If |DeltaT| < 5, then there will be a lot of mixing.

This calculator is a bit more accurate than the approximations above: Water Density Calculator

 

[Guest]

First off, shame on you for wasting all that water

We put the suction hose down in the lowest part of the pool, and then return the clean water back at the spa, if there is one. This seems to keep the clean water separated longer from the "bad" water, and lessens our treatment time as well. We would love to find a way to keep 25-50% of the clean water isolated from the dirty in our process, as we feel that would lessen our run times significantly.

Good experiment (aside from the wasted water! Sorry, but I have to bust your chops on that; it's what we do!). Nice to see someone else thinking, and to validate that there is a difference

 

[frustratedpoolmom]

First off, shame on you for wasting all that water

I hope this is tongue in cheek... we love Mark so no busting his chops allowed....

 

[Guest]

First off, shame on you for wasting all that water

I hope this is tongue in cheek... we love Mark so no busting his chops allowed....

Yup, it is (although I really do hate to see wasted water!). I've learned a lot from his posts, and I need to stay on his good side

 

[mas985]

Thanks for the kind words but I feel that I have learned far more from these forums, including those present, than I have contributed but I won't stop trying.

Anyway, I hate to waste water as well but it is much cheaper than trying to have it treated. Besides, the way I look at it water is never really wasted, just recycled.

 

[chris4150]

Just curious, whats causing your CH to rise so high each year?

 

[geekgranny]

Anyway, I hate to waste water as well but it is much cheaper than trying to have it treated. Besides, the way I look at it water is never really wasted, just recycled.

A very good use for the "wasted" water is watering vegetation, yard, plants, garden, etc. One can always use a calcium trap in line on the hose feeding the drip/sprinkler/etc., systems.

My friend in the Yucatan, who gets all of her water except for drinking, from the underground Cenotes was having extreme problems growing some plants that are not native to her area. She was a major landscaper, in an upscale area of Dallas, so, of course, she transformed her jungle into one of the most beautiful places on earth. The water is EXTREMELY saturated with calcium.

I sent her home with several of those calcium catchers, used primarily for misting systems, and she now can grow many plants that are suited for her climate but not her highly calcified water.

gg=alice

 

[mas985]

Hard fill water and no rain causes an increase in CH. Our rain stops about this time each year and won't rain until next winter. So with solar and lots of evaporation, the CH goes from about 325 after the refill to almost 700. I could probably go two years now that they are starting to treat our water with RO but time will tell.

As for watering the plants, I don't think all that salt (SWG) is good for the plants. Plus at the time I do a refill, it is usually rainy season when the CH in the fill water is the lowest and the plants really don't need much extra water.

 

[duraleigh]

Besides, the way I look at it water is never really wasted, just recycled.

Absolutely! No matter what you do with it, it stays on this planet and turns back to usable water. If it didn't we would have run out by now.

 

[PaulR]

So with solar and lots of evaporation, the CH goes from about 325 after the refill to almost 700.

You need a cover to cut the evaporation, man. Doubling your CH in one year? Oy.
--paulr

 

[mas985]

I have a cover, too much trouble to use it.

 

[chem geek]

That's a great experiment, Mark. Thanks for doing it. It makes sense since diffusion rates when there is little or no circulation are very slow. A key to your approach is to introduce the new water in a way that doesn't induce too much circulation. Using a skimmer is a good way to contain the turbulence within the skimmer itself and have a wide-mouth opening to minimize flow rates into the pool itself. If one didn't have a skimmer in the shallow end, then one could possibly use a container with a long straight edge tipped towards the pool for a long spillover, though ideally having it mostly sit in the pool so that the "spill" distance is minimal.

It's good to know that one can use this approach to minimize water usage. If one didn't have the ability to send the water to waste, then one could still use this approach using a hose to the bottom of the deep end with a pump to remove water, preferably with a wide opening for suction.

It looks like using winter rains for dilution doesn't help you as much as is needed since you only get a little under 15" per year which is only a 25% dilution for average 4.5 foot pool depth (a 3' to 6' pool) or 20% dilution for average 5.5 foot pool depth (a 3' to 8' pool). I get around 36" per year which is enough to get a roughly 50% dilution of my pool water in my 3' to 6' pool. I have an electric mostly opaque pool cover so don't have the evaporation problem. I hear you on the pool cover pain and am so glad we put in the electric pool cover when we built our pool.

Richard

 

[StuartPool]

Ok another theory.
Heat rises.
If you introduce water into the pool that is colder than the water that is currently in the pool, and drain from the top, will it have the same effect? Will the hot water drain first or does heat transfer through the water too fast to allow this to happen.

 

[chem geek]

If you are suggesting that it might be even better to introduce the fresh cold water into the deep end and to remove warmer water from the skimmer, then in theory that would be better for the reasons you suggest since warm water does tend to rise and cold water tends to sink. Mark's experiment tends to show that this effect isn't so huge as to prevent a mostly successful water replacement, but it is something else to think about.

His experiment didn't just have the vertical difference (and imaginary boundary), but a horizontal one as well. Perhaps the effect you describe would be more beneficial in a round above ground pool where it's mostly a vertical difference between water introduction and removal.

 

[mas985]

There are two reasons that I introduced the water to the top and drained from the bottom.

First, with an SWG, the pool water had about 2900 ppm of salt in it which should be slightly heavier than the fill water.

Second, the fill water was about 10 degrees warmer than the pool water at the time I did the experiment.

Because of the salt, I deliberately chose a time where the fill water would also be warmer than the pool. However, I'm not entirely sure that doing it differently would have changed the results much. I just wanted to increase the odds.

However, a pool without salt and slightly warmer water than the fill should be able to do the opposite and fill toward the bottom and skim off the top.