Pressure up from 15psi to 25psi in an afternoon

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Desiato

Desiato

LifeTime Supporter
May 7, 2015
128
Catalunya, Spain
Pool Size
17900
Surface
Plaster
Chlorine
Liquid Chlorine
This is my first proper post after my “Hello from Barcelona” so please let me know if I'm doing anything wrong.

The problem I'm having is that the pressure in my sand filter goes up too quickly. Before I go into what is happening I’d better give you a bit of background.

About 7 years ago the mother-in-law changed the pump and filter. The pool professionals doing the work said that the filter wasn't big enough so changed it to the one in my sig (along with the pump). They also recommended using glass instead of regular sand so she took their advice and went with the glass. 3 years ago I took over looking after the pool from the handy man (whose level of expertise was to throw a few chlorine tabs in the skimmer once a week and rake out the leaves) and in my ignorance I carried on where he left off.

Last year I managed to start the pump with the return valve closed and promptly blew up and broke the screw threaded connector to the sand filter. I emptied the sand, changed the broken part, checked the laterals, half filled the tank, slowly put the sand back in and all went back to normal. The handy man had shown me the pressure gauge on the sand filter and told me that when the needle hits 2 (bar) it’s time to backwash. For two years I followed this advice which translates as 'a post backwash setting of 15psi' and a ‘time to backwash’ setting of 29psi'. I placed my hand in front of the return jets and could feel the pressure was quite low at 29psi and was Ok but not blasting out at 15psi. I mention this because a friends’ jets used to really be blasting the water back into the pool but you’d be hard pushed to see if mine were doing anything at all.

The glass was 6 years old when I put it back in, it didn’t look too bad but I had a nagging feeling that I should probably change it because the pressure kept going up too quickly. After a backwash (for 2/3 minutes) and rinse (30 seconds) the psi would be 15. If the floor had a thin film of dirt I’d hoover and after a couple of hours the pressure would be back at 29psi. Sometimes I’d have to backwash twice a day. I knew this wasn’t right so 2 months ago I decided to change the glass to see if this fixed the pressure problem. I still hadn’t discovered this site yet so just bought the only glass media available from a local DIY store and repeated the process. This time I decided to be more thorough and took out the laterals, inspected them and picked out the tiny bits of seeds stuck in the grooves until they looked like new (no damage). Placed a bowl over the open valve at the top of the filter and slowly half-filled with water using the bowl to evenly distribute it and then did the same with the new glass. I spotted straight away that the level was now much lower than it was when I emptied it. I followed the instructions and only put 80kg of glass in as this represented 100kg of sand but I'm convinced the old glass was at least 100kg (excluding what had been washed away in the alley through backwashing). The new level was just about half full but it used to cover the top return pipe (see link to filter) which would make it nearer ¾ full. Once everything was secure, I started the pump for a backwash and it let out a high pitch whine which had me ducking for cover. This is the first time I had turned the pump on in 8 months and after about 20 seconds it shut up and has not done it again but I've read it’s not a good sign if it does that and something could be on the way out.

Now here is where we get to my point.

Having read here that I should be backwashing much sooner than 29psi I did one yesterday when it was around 23 and afterwards it settled back to its usual 15psi. There was quite a visible brown film on the floor at one end of the pool so I hoovered that up whilst keeping an eye on the pressure gauge. After 45 minutes the pressure had gone up to 18psi (hoovering very slowly so as not to kick up the dust). I then connected up two homemade/Ebay bought 1 micron slimebags (another story), ran the filter and proceeded to top up the pool whilst washing some surface debris towards the skimmer. After 30 minutes of this the pressure gauge had now gone to 20psi. At this point I'm thinking ‘this can’t be right, by all accounts I should do a backwash now but I only did it just over an hour ago!” I then decide to hoover the other end of the pool which looks pretty clean but I wanted to test the new slimebags to see if they would catch anything. I open the side wall valve for the hoover (pipe already connected) and close the bottom drain and skimmer valves and the pressure instantly drops from 20 to 15 psi. I hoovered slowly for another 30 minutes and when I'm done I see the pressure has gone back to 20psi. I open the bottom drain and skimmer valve, close the side wall valve and the pressure has now gone up to 23psi (after 30 minutes of very light hoovering). That was 3 hours ago, I've just checked the pressure gauge and it is now on 25psi (with the slimebags removed an hour ago). I' going to leave it running and check it every hour just to see when it stops going up.

Whenever I open the side wall valve to hoover, the pressure always goes down 4 or 5 psi. If I hoover after a backwash it goes down to 10/11psi and then slowly starts to rise as I'm hoovering. I’m not sure what to make of this but my main question is why after a few hours does my pressure go from 15psi to 25psi? Admittedly it does it this quickly if I hoover but I've read on here that some people backwash once every few months but I have to do it once every few days.

It's probably not relevant but I'm getting small bits plant seeds and ...stuff through the return valves so I have another problem there with either the sand filter (don't think so) or the spider valve (checked it and it seems fine). I'll continue this subject in another thread so I don't confuse things.

So in summary, changing the sand hasn't resolved the pressure issue. The sand filter and spider gasket look fine, there's no leaks that I can see so is there a mismatch between the pump and the filter? Here are the links to their info:

http://pdbdocs.astralpool.com/catalogos/CAT12_BOMBA_VICTORIA_PLUS_AP_101.01.02.pdf

http://www.valgroup.es/carac/37000055.pdf

Any help greatly appreciated (sorry if it's a bit long but didn't want to miss anything out).
 
Well, the only way for the filter pressure to gradually rise is by trapping debris. You could have a low level algae bloom that is helping to clog things up.

What is the diameter of that filter?

Can you post up a full set of test results? What kind of kit do you have?
 
The filter diameter is 640mm or just over 25"

I've only just bought a proper test kit from LaMotte and have only got as far as unwrapping it. I'm leaning away from thinking it's a low level algae bloom as it has been this way for years and the pools always pretty clear. I've also only just changed the sand/glass and with new glass and a fairly clear pool, I see this pressure rise time after time and as I say, it's been like this for years.

I will get a full set of accurate results with the new kit tomorrow but.....I've just dipped a test strip and got PH 7.2, Alkalinity 150, CYA 30, FC 1.5, CC 0.5. Total Hardness 500. Those from a not particularly accurate test strip.

The test kit is a FAS-DPD Commercial 7 kit 7022-01
 
Good to hear that you got a good test kit. :goodjob: I know they can be hard to find over there.

Also that filter is a good size, wanted to be sure it was not too small.

I suppose there is a chance your problems are related to the glass media, we generally prefer sticking with regular pool sand. Although based on that test strip (which we do not trust), your chlorine level is not high enough for your CYA level, so algae is certainly possible.
 
Righto, I noticed the FC and CC was low so I'll throw in some chlorine tonight and see where we are at tomorrow. Just going to backwash first.

I'm also thinking the glass might not be that great. I'm getting quite a lot or dirty water and 'bits' returning to the pool and was going to start another thread about that so as to not confuse the two issues but there's a good chance they could be related.
 
Can I ask a silly question? Can't seem to find the answer, maybe it is blindingly obvious?

When using the test tube, why would I choose the x0.5 over the x0.2 to do the FC test?
 

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Accuracy. When I do a FAS DPD test I usually use the x0.5 unless I am doing some sort of experiment. In most cases you shouldn't really need that much accuracy. In fact, I hardly ever use FAS DPD and rely upon OTO most of the time. But when slamming a pool, FAS DPD is necessary because of the elevated chlorine levels.
 
As the FC was very low I decided to go with the 0.2ppm so I could see exactly how low it was....it didn't even register :(

I've shocked the pool this evening and will do a complete set of results with my fancy knew test kit in the morning. :grin:

Now, the other issue.

After changing the glass a couple of months ago (and backwashed and rinsed) I started hoovering as the pool had been idle for two weeks and needed a good clean. The water was crystal clear so I was feeling very pleased with myself but I was then horrified to see two plumes of white dirt shooting out the return jets clouding up my nice crystal clear pool.....and it didn't stop.

The damage had been done so I just continued to hoover and watched as the return jets filled the shallow end with dirty water until the whole pool was cloudy and I couldn't see the drain at the bottom of the deep end. I checked the spider gasket to see if anything was a miss but it looked fine. One problem I have with my spider gasket is that it is glued into the handle part that you can lift off. Here's a photo of it so you can see what I mean. The gasket doesn't have any kinks, dinks or tears so on the surface it looks Ok.

IMG_0724.jpg

That's when I went on the search for Slimebags in Europe. I found a guy on Ebay in the UK (filterbagman2) who made me 4 x 1 micron bags for £15 inc postage and here are two of them next to the leaf collector for scale:

IMG_0714.jpg

Unfortunately, as others on this site have found, there are things smaller than 1 micron which pass straight through the bags :(

IMG_0721.jpg

When the bag was removed I found something surprising inside, lots of 'bits' along with the dirt.

IMG_0723.jpg

I'm convinced there's nothing wrong with the filter and laterals (having changed the glass twice) but I'm not convinced the multiport valve is 100%. So today I took it off again, gave it a good clean and when I went to refit it, did so with the handle placed between two selections. There's a chance I didn't do this the last time so once it was all tightly screwed back on, I started hoovering some pretty bad dirt off the bottom whilst all the time keeping an eye on the return jets.....they were sending back 99.9% clean water, :party: This intensive hoovering went on for 45 minutes and the shallow end remained cloud free. I then fitted the other two brand new filter bags to get a comparison to the first two, ran the filter for 30 minutes whilst topping up the pool and then hoovered the shallow end for 30 minutes which only needed a light hoovering (was hard to see what to hoover as it was quite clean). I then took the bags off and to my surprise I was looking at exactly the same image as the first two, dirty and full of bits. How did that happen?

I had properly seated the multiport handle which made the first 45 minute of serious hoovering produce 99.9% clean returns so how did a very light hoovering for 30 minutes fill the bag with dirt and bits? I did read someone else say on this site that when the psi goes up, there is more pressure on the multiport valve and this could lift the handle and gasket and allow the bits to get through. It's possible this is what caused the 2nd 'bit infestation' as the pressure had gone up at this point. I'll have to run another test tomorrow with the pressure around 15 to 18psi and see if this theory is correct.

Any other thoughts?
 
After adding chlorine last night, here are the rather disturbing results this morning with my FNTK (fancy new test kit):

CYA - 120
FC - 3
TC - 5
CC - 2
PH - 7.4
CH -880
TA - 150

I was shocked about the CYA so tested again but came back 160 a second time! (the disappearing black dot) To see if I'd caused the change with the added chlorine I did another test strip but it's still telling me I'm firmly in the 30 bracket. if 120/160 is right, this would explain why I've always struggled to keep chlorine in the pool and also why the pressure gauge is always going up. Is it really possible that the filter has been fighting an invisible enemy for years? I'll switch to liquid chlorine and look at bleach as another option to stop the pucks and chlorine granules from increasing the CYA. So many regular pool owners here in Spain must be in the same boat as all you can see on the shelves are endless tubs of Trichlor and Dichlor Tabs and granules. They don't stand a chance at keeping their CYA levels down.

The rest of the results are also out of whack so I'll wait to hear from you guys where to start (but I fear it will be with the CYA, the wife is going to love that! :()
 
Yes, it is not only possible but likely. High cya from pucks is the root cause of many a green pool. Liquid chlorine and bleach are the same thing different chlorine percentage. Bleach is usually 8.25% and liquid chlorine is usually 10% or 12%. In the US that is.
 
The wife was already dead set against me spending big bucks on the test kit and I'm struggling to explain to her that 'just because it looks nice and clear, doesn't mean all is well' so baring any other advice, I'll start by draining a fair bit of the water tomorrow morning (when she's at work ;)) and spend the rest of the day filling it up again. I'll then put some more chlorine in to help balance the CYA to Chlorine levels. Any thoughts on the CH and TA or should I just leave those for now?
 
You can ignore the TA for now.
The high CH can also only be lowered by replacing water ... if you used cal-hypo that could have contributed to the high CH.

So, replacing water to lower the CYA and CH is the correct next step.

Did you do a diluted CYA test to get the 120 and 160 numbers?
 
jblizzle said:
You can ignore the TA for now.
The high CH can also only be lowered by replacing water ... if you used cal-hypo that could have contributed to the high CH.

So, replacing water to lower the CYA and CH is the correct next step.

Did you do a diluted CYA test to get the 120 and 160 numbers?
Click to expand...

We don't have cal-hypo here, just lots of CYA increasing chlorine.

I had to use 50% tap water to get the 120/160 CYA readings as the first time it was off the scale.

Thanks jblizzle, I'll let you know how I get on.
 
Whilst I wait for the pool to refill, I've been shopping around for bleach and reading up some more on the CYA test. I appreciate I am heading off topic as I started off asking why the pressure in my sand filter keeps going up so is it OK to ask questions about bleach and CYA here or should I try and find the appropriate section?

Tell you what, I'll ask them here anyway and can then delete them and move them elsewhere if the mods tell me to.

I just went to 3 of my local supermarkets, Lidl, Carrefour and Mercadona and they all sell pretty much the same bleach. Unlike in the US, none of these sell anything over 5%, in fact all they say on the bottle is "less than 5%" which is less than helpful. What they then go on to say is that they contain between 35g to 37g of chlorine per litre. I used to be OK at maths but trying to divide a weight by a volume has me scratching my head. :scratch:

So the first question is are there any mathematicians out there who can calculate what percentage 37 grammes of chlorine is in a 1 litre bottle of bleach? Once I've got that figured out it should be fairly straight forward to calculate how may litres of bleach I'd need to raise the FC level by 1ppm.....I think.

Second question is to do with the CYA test. As I mentioned earlier, the test strips have been consistently telling me that I am in the 30 range but my FNTK from LaMotte said 120 to 160. I've just been reading about the conditions you should use when doing this test, back to the sun at waist height, and I'm now wondering if this hasn't played a part in my reading. There's no mention in the LaMotte quick instructions (inside the lid) or in the booklet about being outside and with your back to the sun. Can someone enlighten me on how this procedure came about and what difference does it make if you are sitting at a kitchen table at midday peering down the tube from close range because that's what I was doing. I hope I haven't just poured 10,000 gallons of water down the drain for nothing :(

Appreciate your help guys so please keep it coming.
 

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