Is there any way to determine (with a trash pump) how many gallons have been pumped out while draining?

anthonypool89

Gold Supporter
Aug 26, 2016
587
Berks County, PA
I'm considering doing at least a partial drain. The water company I use charges for a minimum delivery of 5k gallons (so I assume I pay for that whether I wind up using it all or not). He can bring 6k to 6500 gallons per tanker. I don't want to wind up having to put in a few hundred gallons (or more) from my well if I'd drain out more than he has with him. So how does one begin to figure out the gallonage pumped out? I can rent a trash pump locally, but - short of eyeballing the level as it goes down - I imagine the pump doesn't have any sort of feature whereby it calculates the rate / gallons pumped out? If so, that'd make things easy. My pool walls taper in all the way around (compared to a square or rectangular shape where the walls are straight all the way down). So that makes it a bit harder to 'guesstimate' the amount pumped out. There must be, proportionately, more water at the top 2-3 feet (where the walls are still basically straight) compared to when everything tapers in (significantly) leading to the drain. Before I'd do this, I need to have a handle on how much to pump out given the 5k minimum delivery and the total 6k to 6500 load. 6 years ago things were easy cause I had the entire pool drained prior to renovation. I really didn't want to drain all of it this time nor have them bring two tankers though I guess that's a possibility. Any advice?
 

anthonypool89

Gold Supporter
Aug 26, 2016
587
Berks County, PA
OK...I think I might have this - somewhat. The rental agency told me their pump is rated for 200-300 gpm. Half of my pool=6,250. So if I use a median figure of 250 gpm, 25 minutes should pump out approx. half the pool. Figuring on the low side - 200 gpm - then 25 minutes would be 5,000 gallons. Going on the high side - 300 gpm - the 25 minutes would be 7500. The level of variation within these still presents a problem for me in possibly winding up having to add 1,000 gal. from the well (in the case of the pump putting out 300 gpm). I'd like to fine tune this if at all possible.
 

Msch99

Gold Supporter
Bronze Supporter
Jun 11, 2018
906
Verona, MO
If you know about the total volume and pool is rectangular in shape then x amount of gallons per inch of water height. 10% exchange = 50% drain in height. Pool information doesn't say whether free form or sloping floor.
 

PoolBrews

Well-known member
Oct 16, 2019
246
The Villages, Florida
This is easy to calculate. Mark the starting time you turn on the pump, then time how long it takes to fill a 5 gallon bucket at the exit stream. Divide the total drain time by the time it took to fill the 5 gallon bucket, and you'll get a very accurate reading for how many gallons you drained.

I've done this twice with my pool, and am usually within 50 gallons or so.
 

anthonypool89

Gold Supporter
Aug 26, 2016
587
Berks County, PA
This is easy to calculate. Mark the starting time you turn on the pump, then time how long it takes to fill a 5 gallon bucket at the exit stream. Divide the total drain time by the time it took to fill the 5 gallon bucket, and you'll get a very accurate reading for how many gallons you drained.

I've done this twice with my pool, and am usually within 50 gallons or so.
That's a great idea, but what was the output of the pump you were using? I'm thinking lower than this trash pump I can rent which puts out @250 gpm. That comes out to a tad over 4 gallons per second, so I'd need a much bigger container, i.e. a 40 gallon container should fill in 10 sec. I'm thinking the strength of the exit stream is probably pretty strong so could just splash out of whatever container I have available. My pool pump is rated at 80 gpm, and I know that's a pretty good stream of water - can't imagine how much 3 times that would be, although the trash pump does come with a 3" hose.
 
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PieterS

Active member
Jul 1, 2020
33
Minneapolis, MN
This is an interesting dilemma! The engineer in me figures you should be able to figure it out from some fancy modeling/geometry of your pool design - but that's not necessarily easy either. Are you mostly worried about stressing your well pump should you overshoot a little bit? Seems like you ought to get somewhat close eyeballing it.

Maybe another solution would be to go with a slower/less powerful pump. Do you really need to accomplish this in 25min? With a slower pump, you could get a much better idea of how much it pumps per minute (I'd check several times to get a good average) and probably get pretty close. I have no idea how easy they are to come by - but there must be flow meters out there, my water softener has one built in to know hos much water has been consumed.
 

Newdude

Well-known member
Jun 16, 2019
4,571
NY
If you are going through all this trouble, Just get a 2nd truck and refill 80% of your water and convert. The conversion will be much easier after that. You are throwing good money at a bad problem. The best you can hope for is to get another year or two before having to do it all again.
 
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anthonypool89

Gold Supporter
Aug 26, 2016
587
Berks County, PA
Hardware store also has a submersible (sump) rated at 63 gpm. Newdude (here on TFP) came across a polygon area determining chart whereby you can plot points on a graph that roughly approximate the shape of the pool and then calculate area, etc., and I've looked at that as an option but would much prefer a more hands-on means of determining the output. The concern, as you correctly surmise, is with the well. I've already put a good amount of water in the pool after doing two 'mini drains' down to the skimmer - and we're pretty dry here of late as it is.
 
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mgtfp

Bronze Supporter
Mar 5, 2020
488
Melbourne, Australia
Maybe not helpful for your problem right now, but what you should definitely do is write down the water level before you start refilling. You'll probably know pretty accurately what you are refilling from that tanker (or tankers, going with Newdude's advice...) , and that will give you a good baseline should you ever have to go through that process again.
 
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anthonypool89

Gold Supporter
Aug 26, 2016
587
Berks County, PA
If you are going through all this trouble, Just get a 2nd truck and refill 80% of your water and convert. The conversion will be much easier after that. You are throwing good money at a bad problem. The best you can hope for is to get another year or two before having to do it all again.
If this was old plaster that I'd be less worried about, I'd be more apt to drain most of it as you say. It does make sense to do that, but I'm just not sure I'm ready to tackle the conversion this summer anymore. I'm already way behind on other projects due to not working outside in the 90+ degree heat. I'll keep thinking on it.
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
7,200
Central California
I'm pretty sure you can't rely on the pump's flow rating for this. Those rates are greatly affected by the overall head (which I barely understand), but I think the length and size of the output hose, the height of the hose and the depth/location of the pump all affect the actual flow rate, which could be wildly different than the rating. If the structure of the pool is not a concern (what happens to it when you remove half the water), then I would just use garden hoses and the bucket trick and just siphon it out. That will be accurate enough and save you the cost of the pump. Just start the drain well enough ahead of time, which you could actually also calculate with the bucket trick (how long it will take to siphon off the amount of water necessary). I used just one hose to drop my pool's water level a couple feet and I don't remember it taking all that long. Put x number of hoses on the job and I don't expect it would take all that long.
 
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Newdude

Well-known member
Jun 16, 2019
4,571
NY
If this was old plaster that I'd be less worried about, I'd be more apt to drain most of it as you say. It does make sense to do that, but I'm just not sure I'm ready to tackle the conversion this summer anymore. I'm already way behind on other projects due to not working outside in the 90+ degree heat. I'll keep thinking on it.
I get it. I do. But with a 200 GPM on the low side you would drain completely in an hour. With the two trucks on standby it would be filled in another hour. 2 hours should be fine in PA and you could stand there with a hose just to make yourself feel better by keeping the sides wet.

Whatever 1500 gallons is left would be an easier conversion than the battle you will still have by staying with Baqua *AND* the 2nd tanker truck will be cheaper than the treating chemicals to make the 1st truck into Baqua water.

you will immediately save money and effort. A week later you will be maintaining the pool for $10(?) a month troublefree. If you still don’t like the chlorine once it’s done properly it will be an easy conversion to salt for next season.
 

anthonypool89

Gold Supporter
Aug 26, 2016
587
Berks County, PA
You bring up something I hadn't thought about and don't recall from 6 years ago - that of how much Oxidizer and Sanitizer it takes to reinstate proper levels for Baqua (starting from fully drained). I don't seem to recall having to add a huge amount. Baquacil instructions (like when converting to Baqua or simply fresh fill) calls for 1 gal. of oxidizer per 10k and a full container (1/2 gallon) of sanitizer....so I imagine that's what I did.
 

Newdude

Well-known member
Jun 16, 2019
4,571
NY
Baquacil instructions (like when converting to Baqua or simply fresh fill) calls for 1 gal. of oxidizer per 10k and a full container (1/2 gallon) of sanitizer.
Ok then that will be much cheaper than I was guessing to treat it. Where does the $1200 a season in chemicals come from then ? Do you have to dump that much in weekly ?
 

anthonypool89

Gold Supporter
Aug 26, 2016
587
Berks County, PA
I did not mean to sound like I was criticizing or trying to correct anything you said - but it had me curious as to just what the start-up amounts are. (My memory is NOT good enough anymore to recall such a thing after six years!) You have to remember - I order aLOT of some of this stuff -about 6 boxes of Oxidizer (4 gallons to a box) - since, yeah - to do it right - once I started using a kit to test the level - it does take more (at least for me) than the maintenance amount listed on the label. Then, I have also been buying the aqua finesse tablets (discontinued those after the Line Clean debacle) and the Ahhsome. It all adds up, along with pH increaser, decreases, filter cleaner, anti-foam, AND all the DE - 75 lbs of it for this season and I suspect that won't be NEAR enough with having to backwash every 3-4 days. It seems I'm going to be back to that routine so whatever is in the water that may have been causing those rapid filter pressure increases was apparently not eradicated from the Line Clean. Given that the last filter cycle went 19 days I was hopeful. Geez...I think I could write a book on all this. Actually, if you put together all my threads and posts of the last - what - 3 years or so? - there's enough there. I have to laugh a bit every time I look at the "well known member" under my username...ain't it the truth????
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
7,200
Central California
I don't know the first thing about Baquacil, or why anyone would want to use it. I do know, however, that TFP methods work and they're all based on chlorine. No complaints here. TFP advice has been so good for me and my pool that I'm now pretty much willing to follow it blindly. If they're suggesting to switch over, I'd go with that. And if you're getting ready to spend (at least) half the money to get you there... Well, I'm just sayin' I know what I'd do. Bite the bullet. Empty the pool and start over with chlorine... And that'll only cost you 2 cents (for my thoughts about it, that is!) ;)