Adding extra return and effect on circulation

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Diver

Diver

0
May 5, 2011
482
South of Boston
I have a 27k gallon IG pool. I have a skimmer, main drain and 3 returns. Here is a diagram:



I have a plugged-in dead return. Near skimmer. It's about a foot away and slightly below the skimmer (ignore construction, it was another story long time ago):



At some point I checked it and it seems like it was leaking. I was bored another day and put together a L shape pvc pipe contraption, screwed it to the return socket and poured some water into it and it seems like it's holding the level just fine. I have few terminated lines near my equipment pad and I assume one of them is connected to this return. Before I do pressure testing and connect it to the pump/filter I would like to better understand the net result on water circulation and mixing.

On one hand I will have 4 points of water injection that should help with mixing. On other hand the overall velocity at the return jets will decrease even though the overall water flow increase will counter that to some extend. So I believe in general it will help with the mixing and circulation. Having 4 returns on high speed doesn't sound like a problem. But I wonder if the exit velocity on slow speed speed will be too low and it would make things worse?

Right now I have 3/4" eyeballs on my returns, but I have 1/2" ones as well. I guess worst case scenario I could go with smaller eyeballs and have things as they are right now, but with 4 injection points instead of 3.

I would point that return towards the main drain since it's right next to the skimmer. Pipes are 1.5" all around

Right now my filter pressure is about 8.75psi and vacuum is about 6 in the pump's wet end. Overall head is 38ft and flow is about 55 GPM (calculated and measured). I assume on low speed the flow is half of it.
 
I don't think having another return is going to make that much difference unless you have a problem with surface debris collecting in a specific area. Plus having a return right next to a skimmer can be problematic unless it is always pointed at the bottom.
 
i would point it towards the main drain. just for the sake of better circulation. i'm thinking that switching to more restrictive eyeballs in conjunction with extra return will keep the flow rate about the same but would help with mixing..
 
Yeah, pointing that eyeball down would be the thing to do so it doesn't effect the simming in that area like mas985 mentioned. Smaller eyeballs would increase the velocity out of the other returns.

BTW, nice avatar

dd
D-17203
 
Diver said:
i would point it towards the main drain. just for the sake of better circulation. i'm thinking that switching to more restrictive eyeballs in conjunction with extra return will keep the flow rate about the same but would help with mixing..
Click to expand...
But that is just the opposite of what you should do. By pointing the return at the MD, it will just improved RE-circulation rather than circulation. The point is you don't just want to go directly from return to MD and bypass the rest of the pool so the same water keeps getting recirculated. Treat the MD as another return because basically, that is what it is but just in reverse. So to get maximum circulation, you would want to point all returns not in the direction of a suction port or another return. But again, I don't really think adding another return is really necessary nor will it make a significant difference in water quality.


i'm thinking that switching to more restrictive eyeballs in conjunction with extra return will keep the flow rate about the same but would help with mixing..
Click to expand...
More restrictive eyeballs will reduce flow rate but increase exit velocity. Again, in this case, it shouldn't be necessary unless you have a dead spot but with three returns, you really shouldn't have that.
 
Mark,

One of reasons I want to improve the circulation is that I seem to have problem with filtering on low speed. I've had the pool for 3 years and first year didn't have a single problem even though it was my first year. I read this forum for 9 months straight prior to opening the pool though. 2nd year I switched the motor on my pump to 2 speed and since then I would get green spots here and there on low speed while all the levels being in the range and water being clean. I suspect that I cut the filtering time too short and that made things worse. I went from 8 hours on high to 12 on low.

I got tired of the green spots and went back to high speed filtering for 8 hours a day and things seem stable. I want to switch back to low speed and I was thinking extra return would help that. I will switch to 24 hour low speed and if things hold up, reduce it to 16 and keep it there.

I got your point regarding directing the return towards the MD, I think I can find a better direction. I understand that I don't have to have the extra return, but I like doing small pool projects like that and if there is some fringe benefit from it, why not, right?

As always, thanks for your input.
 
I don't think that has anything to do with run time or circulation. What you are describing is usually due to low FC levels. Too many times I see on this forum, people trying to solve chemistry issues with run time and "circulation". Yes, some circulation is need but you can't compensate for low FC. The run time my pool which is close to your size on 4 hours per day and 3 of those hours are on low speed.


What is your normal FC and CYA levels?

Have you tried an OCLT?
 
Mark,

Right now my CYA is 45 and on the last 3 instances that I managed to need to SLAM the minimal FC level was 5.5 in between SLAMs. Meaning I didn't let it go below 5.5 any time between the time I had to SLAM. And normal range for 45 CYA is 4 to 8.

However I have suspicions I might had MA, so it would explain why I would get green spots coming back at 6-7ppm levels after SLAMINg. It would always start in the shady areas. The OCTL would clear overnight right after I would start shocking at the end of the day. Basically I would start the process at 7pm, check the levels at 10pm and at 6am next day and it would be within 0.5ppm loss and no CC.

I did a proper MA SLAM recently and my minimum FC levels now are 6-6.5 ppm with a target of 7-8ppm.

I check the levels daily at the end of the day (that's my minimum level) and add chemicals to my target levels. I even got the calibrating 50ppm CYA solution since I started to question my CYA readings.

My timer/switch only allows me to run the pump either on high or low. I can't run for an hour on high and the rest on the low like you do.

I will see how it goes after MA SLAMing and I will keep the pump on high for now.

The dead return has a matching terminated pipe in a very awkward place for me to access, so I might let the project go anyway..

Thanks for you help.
 

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Well, I’m gonna be a big man and admit that most of my problems were self-inflicted and also chlorine level related as it was earlier alluded.

I combed thru my xls for 4 years of my pool ownership (previously I stated that I had it for 3, that was a mistake) trying to find some patterns. I didn’t come up with many, until I changed few things in my spread sheet:

- I recalculated CYA levels assuming any trichlor added had immediate effect on CYA and it didn’t take until it all dissolved
- When CYA was calculated as function of trichlor added, I recalculated for 25k for pool volume since that’s the lowest volume my pool can hold while skimmer is still functioning. Before I always used 27k since I believe that’s what my pool capacity is.
- I retroactively recalculated derived CYA levels for years when I was told my pool was 30k.
- I made sure that every time my measured CYA was in between 2 readings, I used higher value for safe FC levels

With all that in mind, a new picture emerged. First time I open the pool in 2011 it had a CYA of 40. Mid-way thru the season I added 5ppm of trichlor to bring it back to 40 to compensate the loss of CYA due to backwashing. This was the only time I did anything with CYA that year. And I didn’t have to shock the pool once. I touched the low range of FC once, but I was spared. There was not much variation in the CYA levels and maybe as results that year was problem free.

In consecutive years the range of CYA levels were more broad since I would start with lower levels at the beginning of the season (I didn’t using trichlor exclusively as prev owner did) and I would bring it up to 40-45 using trichlor thru the first month of the season. I could see now that I drifted lower on some the occasions with new CYA levels calculated as mentioned above and that seems to have resulted in problems.

I will use the approach to calculate the highest level of CYA that I could possibly have at any given moment and use mid-range of FC levels as my new minimum FC level.
 
Even with backwashing CYA should not be changing that quickly. A typical 1 min backwash at 70 GPM would use 70 gallons of water and once refilled, should only dilute by 0.25% or 0.09 ppm for a CYA level of 40 ppm. How often do you backwash?

But the bigger question is why are you calculating CYA and not just measuring it?
 
Since I had a lot of instances where I had to shock I had to backwash 5-6 times a season (~4 month). I also had a small leak and plenty of rain. Looking at the data I have, I typically lose 5ppms of CYA once or twice per season, so there is not that much loss of CYA.

I didn't mean to imply that my CYA goes up and down widely thru my season, it just I didn't account for it properly when I was raising it.

As for CYA calculations, I would measure the levels and then would add ppms to that number as I add trichlor. I would measure it here and there as well to make sure it's where I expect it to be. Since trichlor adds a known amount of CYA with proper calculations I could know my worst case scenario. If I measured CYA at 30ppm and added 5ppm worth of trichlor, my CYA can't be higher that 35ppm. The key here is proper calculation and as I mentioned above, some of my assumptions were off.

I have 16 oz of CYA testing reagent so I could test it every week if I want. But it would be great if CYA test would remove subjectivity out of it. At this point I could tell that my CYA is slightly lower that 50ppm calibrating liquid. However, I could measure it several times and end up with slightly different readings. So I will use the highest reading from now on and not the mid-value to be on a safer side.
 
I'd use that return as the suction for your waterfalls (you were the one with the waterfall problem right?) If not, Ignore me :p
 
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