No drain water exchange - use autofill?

[BenB]

Hi everyone!

This is probably a really stupid question, but if I have an autofill and it's positioned in the shallowest end of my pool, then am I ok just use that to perfectly balance the water that is pumped out of my pool, as opposed to using a hose and matching the flow rates?

This method appeals due to being in hot California, with a plaster pool that I don't want to damage while draining, and because I match the criteria listed in the blog post - salt water pool with high salt and CH levels being the reason for the exchange.

Thanks!

 

[mknauss]

Normally an autofill puts the water down about 8-12 inches from the surface. So it would not be a good idea to use it at the start.

Also, they normally also will not give much rate. So once you have exchanged enough water to get down below the autofill entry into the pool, you can use it, but you most likely will need to supplement it with a hose anyway.

 

[BenB]

Thank you for the input and probably record breaking reply time!

Can you clarify what you mean by "puts it down 8-12 inches"? Mine sits there whistling all day seemingly replacing evaporated water drop by drop constantly. Is that not normal?

 

[mknauss]

The entry into the pool. Is there not an entry port for the autofill water below the surface of the pool water?

It dribbling all day is correct.

 

[BenB]

Ohhhh I see what you mean. Yes the outlet is on the side wall down a bit as you describe. But if it's dribbling all day and the water level never drops, then wouldn't it also continue to fill even before the level hits that line on the pool when doing a water replacement? It's not waiting for the pool level to drop that low before doing its thing normally.

High school physics and water was a long time ago. Sorry if I'm missing a very simple thing.

 

[mknauss]

When you exchange, assuming you will draw from the pool at the deep end and add at the surface, you want to keep from mixing the two waters. When you start, if you add water at the autofill, you will be mixing the waters below the surface.

Once you have exchanged enough water to have the new water below the autofill entry, you can start using it to add water to the pool.

 

[BenB]

Thank you again! Is there a consensus on fast vs slow replacement? I assume we're also trying to "out pace" regular diffusion between the old and new water. So are we trying to swap the water as quick as possible but without causing too much disturbance that would cause mass circulation and therefore dilute everything?.

 

[mknauss]

Correct. Most household systems can add water at about 7-10 gpm. A 1/2 hp sump pump using a 3/4" hose for the effluent can pump at about 7-10 gpm. It is imperative to have the pool pump disabled during this process. It is not perfect. Efficiency will depend on how different the two water characteristics are.

 

[BenB]

Thank you so much for all the replies.

Last question - for tonight anyway haha - since the pump will be off for potentially days, yet we want to avoid mixing water, should we bring up the FC high such that there is enough to last a few days, or since we're pumping it out is that a waste of time and liquid chlorine? Do we just cross fingers that nothing grows in the exposed period of time? Or is it a mandatory SLAM to be certain once it's all done?

 

[mknauss]

You are draining for CH level. What is your fill water CH?
You can add some chlorine to the surface stream once or twice a day.

 

[BenB]

Fill water CH is, thankfully, only 100-125.