Backwashing Problem.... Water flow reducing during backwash

[NmX]

Hi everyone! I'm Jason, long time fan, first time poster.

Problem: While backwashing filter flow starts full, then within seconds, slowly starts to reduce until water flow coming out is about 1/2 to 1/3 of normal during backwashing (which typically maintains the same high flow throughout the backwashing process). Flow does NOT reduce when running in RINSE mode or in WASTE mode. Only happens in BACKWASH and starts off high and reduces quickly. Haven't backwashed in about a week or two, never happened prior to today. Pressure before backwash wasn't not very high (just touching yellow area, forgot the PSI exactly), but lower than when I usually backwash, but since flow seemed low as evidenced by my skimmer not skimming due to lack of sufficient suction, after first checking all grids and lines, figured it must be the filter needing backwashing. It's skimming now, but not impressively so, but clearly backwash helped a little at least on that end.

Pool: Intex 22' UltraFrame above ground pool

Filter: Intex Krystal Clear Sand Filter Pump for Above Ground Pools, 3000 GPH Pump Flow Rate, 110-120V with GFCI

SWG: Intex 120V Krystal Clear Saltwater System CG-28669 with E.C.O. (Electrocatalytic Oxidation) for Above Ground Pools

Skimmer: Intex Deluxe Wall Mount Surface Skimmer

*Amazon links provided for equipment clarity for the same of specificity.

Skimmer basket and inlet lines and filter grids are all clean. Considering that RINSE and WASTE water flows are fine, I'm guessing pump and lines up to the filter are all good. After backwashing, PSI only dropped 1 or 2 psi after, still remains kinda high... (just below the border between the green and yellow areas on the gague). It morally sits around half way into the green after backwashing.

I played around switching between backwash, rinse, recirculate, waste, etc.... but to no avail.

Pool and pump is 1 year old, filter is about 8 months old (but not run for 5 months during winter). SWG is about 1 month old.

Thank you for any help!

Jason

 

[Texas Splash]

Hi Jason, and welcome to TFP There's a few things in your post that caught my eye, so I'll run them by you here:
- You mention "grids" a couple times, but also state you have a sand filter. So it is indeed sand correct? When was the last time (if ever) that you did a deep cleaning like that seen HERE?
- How are you testing your water? What does the water look like (clear, cloudy, tinted, etc)
- Knowing your baseline (clean) psi is very important. Here at TFP, we don't judge backwashes so much on the factory markings of the gauge, but rather has the psi increased 25% from the clean/starting pressure?
I understand your pump/filter are not that old, but depending upon the condition of the water and how it was tested, the issue could be related. It's always best to rule-out the easy things first (water test results, exterior appearances, etc) before having to open things up.

Stick with us and feed us more info. We'll all pitch-in to help get you back on track. Nice to have you with us.

 

[NmX]

Texas Splash,

Thanks for the reply.

I do have a sand filter. The "grids" I was mentioning cover the water inlet ports on the interior side of the pool. They have large holes, maybe 1/8" or so, and I'm assuming are there to stop large debris from entering the pool. The skimmer basket has a tendency to suck debris through it (tiny pedals, etc) and they can accumulate on that grid which can nearly eliminate the water flow into the pump. I added a mesh sock around the in-pool skimmer basked which helps a lot with that, but doesn't eliminate it. I'm going to try adding some pantyhose instead for a finer mesh which should keep the grids entirely clear at that point.

I test my water in three different ways. I use an occasional dip test strip, but only to get a weekly general reading on CH, CYA, and TA. I also use a stick type test for salt levels. Second, I take the pool water to the local hardware store for a computer based test once or twice per month. Third, I use an OTO test 4-5 days per week to test for TC and PH. Currently they are at 5-10 and 7.6 respectively. TC is high right now cause I've been playing with the SWG run times but don't want to let the TC crash while I figure it out... so slowly reducing it since it's not like we're swimming in it yet anyway. Still been a bit chilly. Water looks pretty though! Couldn't get it this clear for more than a week or two at a time last year, but learned a lot since then so hoping to avoid that fight!



The clean PSI is normally around 6 and gets backwshed at about 10.5-12. It rises about 5-6 psi between backwashes, and if memory serves the manual says to backwash at 8-10 psi increase, but I've never waited that long. Highest I've ever seen it is about 12, and I normally do it at about 10.5-11 psi or so.



I just went to the pool and took a video in case it's helpful... I think you can see the flow reduction I'm talking about in the video.

https://drive.google.com/file/d/0B6m7jQJ-1mTJVlROQm9jTTZydTA/view?usp=sharing

I forgot to video the pressure gauge after backwash, so I took another picture. This picture is only about 15 minutes after the original pictures above and is immediately after recording the video.



Took me an hour to post this reply! LOL! Hopefully it'll all help! Thanks again for taking the time to help me. I really appreciate it!

Jason

- - - Updated - - -

Still confuses me why the flow starts good and ends low... I can understand if the flow as low due to a water inlet issue on the pump side, but like I said, starts good in backwash and then reduces... no reduction at all on waste or rinse modes. Just weird to me.

 

[Texas Splash]

A couple things I would recommend that may help:
1 - You really must try to order either a TF-100 or Taylor K-2006 test kit. The test strips are practically useless (except perhaps salt test strips), and pool store or in your case hardware store, tests are not much better. The OTO is fine just so you that you do have some FC (Free Chlorine), but you aren't really able to determine if it's FC (good stuff) or Combined Chlorine (CC) which is in transition and requires oxidation from the sun. One of the most important tests you need from those kits is for your CYA. If your CYA is too high, then what seems like a high FC to you right now may not be high enough thereby allowing more organic material to thrive. It may still look somewhat clear, but your filter can get clogged much quicker.

With a clean psi of 6, I would estimate the time for your 25% increase backwash would be about 7-8 psi (12 psi would be 100% increase, 9 psi about 50% increase, etc). That may seem odd, but it's probably because of the gauge itself and the way it either measures psi or how the numbers are laid-out in design. My factory gauge is the same way. Next time I need to replace my gauge I will order a nice one from TFTestkits.com that uses better materials inside & out.

In any case, it sounds like your filter is struggling to keep-up. A strong start followed by rapid decline in pressure if a good indication of that. But only the TF-100 or Taylor K-2006 will confirm. I hope this helps a little to resolve your issue. If you still have some concerns about your set-up or water conditions, please reply back and let us know.

 

[NmX]

TS,

I really appreciate your reply. I apologize in advance for my confusion on the following points:

1. I have an HTH test kit for TA and CH... but my CYA juice is gone... so I'm due for buying a new test kit anyway, so I'll save up for one of the two you recommended. The Taylor has been on my Amazon wishlist for awhile now, so I'll probably pull the trigger on that one soon.

2. This is going to sound really confusing and contradictory... but last summer my clean pressure was around 9 psi. This year, don't know why, my clean pressure was starting at around 6 psi. No clue why the difference, but the current clean psi is similar to what I used to get last year, so washing at 11-12 should be about right. Not sure why for the last month or so the starting pressure has been lower, but I was taking it as the "new normal". I'm clueless.

3. I'm still confused about the rapid decline in pressure. If the pressure doesn't drop in rinse or waste indicating the pump is pumping plenty of water, and if the pressure in backwash is good to start (when the sand is its dirtiest) and slows when the water is the cleanest (indicating less resistance I would think), and historically it's never done that (maintained full pressure on backwash with same pump and filter), I'm at a loss as to why. As the video indicated, water clarity during backwash is good indicating media should be clear, I kind of still don't know what to do. I've taken the pool from green to blue many times, and other than more frequent backwash, there has been no pressure loss. Even this year, when going from green to blue, there was no pressure loss. This hasn't happened until the last week and the pool has been clear the whole time.... I hate being so pool stupid!!!

Sorry for the further questions. If I'm missing something I apologize.... just still kinda confused.

Thanks again.

Jason

 

[Texas Splash]

Jason, ask all the questions you need. Not a problem. Pool symptoms can stump us all at times. Since you can't post a full set of test results yet other than what you have with the HTH kit, it does make water analysis a little tricky, and that's a BIG part of our equation right now. But everything so far seems to point back to the filter. The higher restriction of flow is understandable when the pump is trying to push/pull water through the sand if it's dirty or covered with an organic material inside. Waste flow being easier makes sense because water is not even toughing the sand. Your pump is fairly new, so you wouldn't' think a deep cleaning would be needed yet, but it's always an option. Doesn't cost anything. Also, do you recall what type of sand was used? Do you know for sure if it was loaded with #20 silica sand? Aside from those things, I think confirming the test numbers is our biggest question at the moment. If you get any other odd indications with your equipment between now and time your are able to get a kit and post a full set of numbers, please let us know, and we'll try to put I all together to see if we're missing anything.

 

[NmX]

Ok, I ordered the Taylor test kit... should have it probably next Tuesday or so! I did buy #20 silica pool filter sand. I might try doing a deep cleaning in the interim just to see... I haven't popped the head off the unit yet either to see if there's anything there to see or not....

 

[Texas Splash]

Great move Jason. Good luck on the deep clean. We'll watch for more posts later.