Optimal depth for returns?

[pjt]

Is there an optimal depth below the waterline where returns should be installed?

Would there be a benefit to having a couple returns at the bottom of the pool to help with circulation?

 

[ajw22]

Is there an optimal depth below the waterline where returns should be installed?

12" to 18".

Recommended depth for the pool line

Hello, this is my first post. I am a happy owner of a salt pool in Phoenix AZ. My brother called me from NCal and is having his vinyl lined pool reconstructed. Are there any regulations or can anyone recommend how far below water line the return line should be? His pool is approx. 9ft deep...

www.troublefreepool.com

Would there be a benefit to having a couple returns at the bottom of the pool to help with circulation?

Some people feel it can help evenly heat a large pool with warm water rising from the bottom of the pool. I can tell when I swim in my 50' pool that has 3 returns on one side when I swim from a warm plume out of a return to a cooler area of water. It does not bother me that I would add the complexity of floor returns.

I don't think floor returns makes any noticeable difference in circulation. Good placement of skimmers and returns on the wall is all you need.

 

[tenderfoot]

Additionally my opinion is that you need to make sure you have enough returns so that these can create movement all over the pool without having any "dead" spots.

 

[uosuof]

Would there be a benefit to having a couple returns at the bottom of the pool to help with circulation?

I have no clue if there is a scientific basis to this but... if one has a few returns 12-18" below the surface, angled so they circle around surface water for the skimmers to work, and the skimmers suck away those top 2" or so of surface water.... then, it would seem to me that the system puts in warm chlorinated water just below the surface and then sucks away that same warm chlorinated water... and most of the pool water below that doesnt get as much of either heat or chlorine.... perhaps particularly so if you have a SWG where the chlorine comes out of the return at the top of the pool and then gets pumped out through the skimmer, rather than swirling around the entire body of water...

Is there any truth to this? In my mind it makes some sense....and if it does, then adding bottom/deeper returns would be beneficial... but perhaps heat and chlorine dont circulate that way in water? Pls someone smarter correct me, thx!

 

[mknauss]

The pool water does not stay that well segregated, especially when moving.
Also, sodium hypochlorite (liquid chlorine) is hydrophillic. So it disperses throughout the water column fairly efficiently.

 

[uosuof]

The pool water does not stay that well segregated, especially when moving.
Also, sodium hypochlorite (liquid chlorine) is hydrophillic. So it disperses throughout the water column fairly efficiently.

Okay. Does pool size / water volume impact your assessment though? I can see how in a smaller pool, 2-3 returns can create enough movement for chlorine to disperse and mix up in the entire water volume. But how about with 20k+ gallons with 7' or 8'+ deep end? that's a lot of water there.. if you are injecting chlorine at the very top surface of that pool, moving it fairly fast towards the skimmers and then siphoning that same top water away through skimmers, does the chlorine have a chance to disperse as well in the bottom/deeper half of the pool? I really don't know any better, and perhaps I am totally off base here... but it would seem to me in this case that your top half of the pool might get much more chlorinated than the bottom half (in turn allowing for more algae etc...)..? I appreciate your answer, but would really like to understand this better.

 

[mknauss]

The chlorine disperses readily. We recommend running the pump for at least 30 minutes after addition to ensure it getting well mixed.

 

[uosuof]

The chlorine disperses readily. We recommend running the pump for at least 30 minutes after addition to ensure it getting well mixed.

I don't mean to sound like I'm not listening... and I am asking questions here to seek answers from expert folks such as yourself, so your answer is truly appreciated... but I like to think part of my brain still functions and I am looking to understand why this is the way you are saying it is... so repeating that it will be fine because it just works that way doesnt help me! I am hoping someone can help me /point me in the direction of scientific theory or empirics I can review and understand..

Sure there is a point where if you inject chlorine through returns at high RPM/flow rates at the very surface, and suck it back out quickly through the skimmer with strong suction, the chemicals go largely in and out and if you have a very large and deep pool, the bottom of that water doesnt see a lot of chlorine.... I am assuming it depends on how close returns and skimmers are, water volume and velocity, but if your flow moves the chlorine coming out of your returns faster than it dissipates into the water, then it can't be good... IF that is the case, I cannot see how running the pump for 30 minutes means anything. If you have a SWG, and a pump that runs even 24/7, but you push chlorine in and suck it right back out around surface level before it fully mixes in with your bottom water... that's no good. Maybe that is indeed why folks get algae on the floor of the pool..

I suppose it is also hard to say because standard practice is to test your water by taking a sample 18" below the water line. I do wonder what the results would be if you had a 20-30k gallon pool and tested a sample 8-9' deep under the water line..

Again, if anyone knows and is willing to point me in the direction of a scientific rationale I can study and understand, that would be hugely appreciated. I get that on this forum there are lots of really smart and knowledgeable folks, but just saying it "believe us because we all say it works this way" doesn't work for everyone - it's more faith than science - and I am just trying to learn the ways of the water...!

Many thx!

 

[uosuof]

I do wonder what the results would be if you had a 20-30k gallon pool and tested a sample 8-9' deep under the water line..

Thinking again about this, in fact, if folks with large/deep pools would be willing to dive in a little and indeed take a sample in the deeper end, I would think that would make for an interesting experiment.. empirically validating how evenly chlorine disperse in water.... and it would be cool to control SWG chlorine production vs liquid chlorine which may disperse more evenly. I would think ppl here would like a good controlled experiment!

 

[jimmythegreek]

I've actually done it from deeper and bottoms and little to no difference in chemical readings. Chlorine mixes very well you can even dump amd brush pool very well amd have good mixing properties. As for returns a single return down lower on wall pointed down will mix the water in deep end better than nothing bit water heats amd cools itself. The basic property of btus amd hvac theory are similar. With AC you dont cool the air, you actually remove the heat and humidity from it. Same with water. The warmer water leeches to the colder water although with no circulation or poor circulation you can have spotty temps

 

[HermanTX]

Sure there is a point where if you inject chlorine through returns at high RPM/flow rates at the very surface, and suck it back out quickly through the skimmer with strong suction, the chemicals go largely in and out and if you have a very large and deep pool, the bottom of that water doesnt see a lot of chlorine.

I think you are overthinking this. One way to test this is to put dye in front of your return and watch how it disperses. It does not "shoot" directly to the skimmer. With 3 -4 returns pushing water out in different parts of the pool, there is a lot of mixing occurring. It is not visible to the eye but put some dye in and you can possibly see it before it becomes too diluted.