Gradual Draining Question

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gilbee

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Mar 31, 2015
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Harvey, LA
Since it's looking like I have to drain some (most) of the water out of my pool, I'm looking for ways to not do a drastic full empty/refill process due to my concerns about the water table under the pool...I noticed that my pump going to the filter has a hose bib on it with a water hose attached...I'm wondering if it makes sense to simply put a city water hose in one end of the pool and open this bib on the pump and let water go in as water goes out. Does this make sense, and will it actually swap the water rather than simply pull out the water that I'm putting in?

Obviously, one has to consider what the gpm output of the pump is vs the gpm input of the city water, but assuming there was relative parity (or that I turned the pump on and off in a regimented fashion), is this an efficient and safe way to approach this?
 
Yes, draining while filling is fine, especially for lower percentage replacements, say 70% replacement or lower. You often need to be around to adjust the flow rate +- a little, but that is simple enough.

This approach ends up using a little more water than draining and then filling, but for say a 50% water replacement it is only just a little more water. On the other hand, trying to do a 90% replacement this way ends up using quite a bit of extra water.
 
Draining and filling at the same time - fill hose in the shallow end and running from the main drain through your pump to waste will work, but will slow the process and require slightly more water. You should try to start and finish this fairly quickly to get the best bang for your buck.

Small drains (anything less than 10-12 inches) will drag out the process and cost you more in time and water in the long run. Removal of the greatest amount of "offending" water, with quick replacement of good water, is what you want here. Stated in another way, replacing 2% of the bad water is still going to leave you 100% of water that is above the CYA level you want. The biggest impact will come from the largest drains you can do each time. Do some searches here for safely draining based on your pool surface type and you will get a good idea of the recommendations to leave some volume in the shallow end depending on your local water table.

You can use the pool volume calculator at the bottom of the pool calc page http://www.troublefreepool.com/calc.html to determine how much and how many drains you should do to lower your CYA (i.e., in a 16x32 rectangular pool 1 foot of water is 3800 gallons. If said pool is an average of 5 feet deep it holds 19200 gallons total. Draining and replacing one foot (3800 gallons) would lower the CYA 'approximately' 20%.)

Hope this line of thought helps in your plan.
 
jtaves85mcss, simultaneous draining and filling does take a little more water, but it actually goes more quickly. It takes roughly half as long, since draining and refilling happen at the same time instead of sequentially. It is also far safer, with no risk of the pool popping out of the ground or the liner floating (if you have a liner).
 
It sure beats the pool popping out of the ground too. And honestly LA has plenty of extra water. I would absolutely not risk a pop out, especially with all the rain lately. Good luck Gilbee, keep us posted!
 
Ok, so I started this today at 9:15AM

the white hose going across the spa is coming from the hose bib on the pump, and the green one going into the spa next to the bucket is coming from the house water line. I tested with the bucket, and found that both are putting out around 5gpm (the house water line puts out about an inch more in the bucket per minute than the pump out of the pool). At that rate, 300gph. I put the supply hose into the spa in hopes that less fresh water would get sucked down the main drains of the pool...is this not a good idea?

refill1.jpg
 
So far, so good...pumped for 8.5 hours today, which is 2550 gallons of what I hope was mostly offensive water since I was only pulling from drains on the deep end and putting in via the spa on the shallow end. Figured it probably didn't make sense to test CYA right after I stopped pumping, because the water hasn't had a chance to mix at all and I may be testing pure fresh water...also the bottom is about to fall from the sky, and didn't want to get caught in it. I'll test tomorrow and see what good today's pumping did.
 
With all the rain is it possible for you to "harvest" rain water from a roof gutter? I was doing that for a while and in a good rain could fill the pool almost to the coping. Then drain to waste and start again. Free water is always a good thing.
 

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Definitely possible, though not sure I'll go that route...not sure how clean/dirty the gutters are, and wouldn't want to contaminate the pool with whatever might be in there....If I knew the state of it, I'd be more willing to give it a go, but it's a good idea.
 
Little discouraged...so, I've now pumped for 18.5 hours (8.5 yesterday and 10 today) at 5gpm, which equates to 5550gal of water. With the pool being 17400gal, that's a little over 30% of the water. My original readings were over 200 for CYA (not sure how much over, didn't dilute a second time), now I *think* I got a reading at 180...poolcalc says that I still need to replace 78% of the water at that rate to get me to 40...so I have a question...when I am finishing a day of this, can I immediately test for cya and get a reliable reading, or do I need to stop the drain/refill that I'm doing and let the water circulate a bit before I take a cya reading to see the actual effects? I noticed my FC took a dive (still at acceptable levels, dropped from 24+ to 12, though I wasn't checking it daily because I knew it was high and was letting some of it wear off anyway) and I added some liquid chlorine to bring the FC back up to 17, so I do see some effects of the drain/refill, just not the drastic change I was hoping for.

Then again, 30% swap may actually have equated to a 30% drop in CYA, and I just didn't know how high it really was...I dunno.
 
It wouldn't hurt to run the pump for 30 min or so to circulate in the new water just to be sure it is mixed in. Bummer! But, you'll get there and it will definitely be worth the effort!
 
gilbee said:
Li can I immediately test for cya and get a reliable reading, or do I need to stop the drain/refill that I'm doing and let the water circulate a bit before I take a cya reading to see the actual effects?
Click to expand...
So if you were able to keep the new water and old water somewhat separated (fill at one end and drain at other), then you can't really test for dilution until you mix the two parts of water. If you mix the two parts, then any more dilution will be again diluted so not as effective and will require much more water to reach your target dilution. I have done this several times before with much success but I usually trust the math and wait until I know I have added the appropriate amount water and it seems to work out pretty well. I get very close to my target dilution but again, you have to make an attempt to keep the two parts of the water separate and avoid any sort of mixing.

You haven't been discharging any pool water back into the pool from the pump have you?
 
I can't help but discharge some back into the pool...I have a cartridge filter and a hose bib on the pump...there's no way to close off the return completely in this arrangement. Basically, I can pump out of the hose bib, and what doesn't go out the bib will either go to the filter, or will go to the dedicated return for the Polaris.
 
Then the water replacement will not be very efficient and you will end up wasting a lot of water getting to your target dilution.
 
Unfortunately, that is my only option, as the water table is too high here to safely drain any other way. Even pool service companies have refused to attempt it until 10 days of no rain has passed (which in Louisiana this time of year simply doesn't happen), so a gradual refill in this way is my only perceived option.
 
Are you apposed to any plumbing mods? Adding a 3 way valve would allow you to redirect all the flow out of the pool.
 

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