Drain & Fill Question

I've been draining & filling to lower CYA. Lately, with Ernesto & following rain showers, I have been draining while Mother Nature refills :D . I've drained a few inches at a time while there is a break in the rain. My question: Is it more effective to drain half way and fill or drain in smaller increments and fill? I figure you get more bang for the buck by doing one big drain, but my waste water winds up going down a slope into my neighbor's yard. Being a good neighbor, I don't want to make his yard a marsh. Maybe the real question is whether the incremental drains are effective at all?

incremental drains do work, albeit..slowly..are you that high? if i was in your situation and had a drainage to neighbor concern, i'd either talk to him and let him know it's a one off, relocate the drainage so it isn't an issue or...do the best you can do with small incremental drains.

Our water used to drain to the neighbors yard too. They never once said anything, but we didn't really like having to do that. Then I realized you could get 50 or 100' foot backwash hoses. I never knew that. Duh! Anyway, now we drain around the garage and down the driveway into the street, where it flows right to the storm drain.

You can do a "continuous" dilution where you add water and drain it simultaneously (presumably allowing for mixing, so you could add water at one end and drain it from the other), but as was pointed out, this is slower. Specifically, to dilute by 50%, you would need to replace about 69% of your pool water. To dilute by 70%, you would need to replace about 1.2 times (120%) of the volume of your pool. To dilute by 90%, you would need to replace about 2.3 times (230%) of the volume of your pool.

Richard

NJ, have you considered the 'sheet method' which has been advocated here? (Place a sheet of plastic over the entire pool, pump the 'unwanted water out from under the sheet while simultainiously putting the fresh fill water on top - it allows you to keep the water level up without the dilution that Richard addressed). As Tenax wondered, how high is the cya and at what level do you want it?
Richard, thanks again for your knowledge and willingness to share it! (I actually didn't have to reach for my old chem textbook, nor the bottle of asprin ;) , to understand this one:) !)

Here is the answer to your prayers.:D

Silage Tube ---- Yep, those big tubes that farmers blow cattle feed into for storage and feeding in the winter. You can buy them at most farm supply stores and they are available in various sizes -- 6, 8, 10, feet diameter and bigger they come in up to 8mil thick --- the way I figure it you could close one end --- lay it across the water of your pool and fill it with water. A 6' diameter 20' long tube should hold 565 cubic feet (3.1416 X Radius Squared X Length X 7.5 gal per cubic foot) which is equal to 4237 gallons ).

Water seeks its own level so the excess will go out the overflow or over the edge if you get a tanker to fill it with a big hose.

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Originally Posted by waste

Richard, thanks again for your knowledge and willingness to share it! (I actually didn't have to reach for my old chem textbook, nor the bottle of asprin ;) , to understand this one:) !)

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I must be softening a bit. The formula for how much pool water is needed to achieve a level of dilution using a continuous flow method is

% of Pool Volume = 100 * LN( 1 - (% Dilution / 100) )

Got a reputation to keep, you know.:eek:

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Originally Posted by chem geek

% of Pool Volume = 100 * LN( 1 - (% Dilution / 100) )

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Drawing a blank ---- What is "LN"

You do not need to worry about your rep EVER!!:)

LN is probably from the French for "Logarithm Napier" otherwise known as natural logarithm which is a logarithm using a base of "e" (as opposed to 10 which is also a common base for logarithms). LN is also the abbreviation used in Excel formulas for the natural logarithm (base "e") so that's how I remembered it.

Draining and refilling is simple:

If you have 20,000 gallons and your CYA is 100ppm, you need to dilute your water by half to get CYA to 50 ppm. By hook or by crook, you have to replace 10,000 gallons, whether slowly or quickly. If you drain 100 gallons at a time, you'll have to do that 100 times.