Have to backwash weekly to maintain flow for heater and SWG... can't figure out what's wrong!

[m_apple]

This our second season with our IG vinyl lined salt pool with sand filter. Every since it was installed, the water level in the pump filter very slowly lowers over the course of a week, with the heater and SWG eventually noting a low flow message. After I backwash, it returns to a full pump filter and the process repeats itself over the next 6-10 days. The robot vacuum cleans the pool regular (we don't get a ton of debris) and I empty the skimmers every couple days. The pool company has checked for air leaks in and around the pump and it appears sealed. The sand filter pressure normally sits at 16 and after a week when it needs backwashing again it only goes up to 18 so not a significant pressure increase.

I'm at a loss trying to figure out what's causing this as it doesn't seem like it should be normal. There's no issue with the jets and the skimmers appear to be doing their job, although after a week when it needs the backwash the skimmers are barely pulling water.

Hoping someone has some thoughts! I'm wondering if it could be an issue with the sand filter, or after the sand filter.

 

[Jimrahbe]

m,

You have the classic symptoms of having algae, even if you can't see it yet. Your filter is doing what it was designed to do..

My guess is that you are running your FC at 1 ppm or less and have almost no CYA in your pool... Any FC your cell makes is being quickly consumed.

You need to do what we call an Overnight Chlorine Loss Test or OCLT. Overnight Chlorine Loss Test

You should also take a good read through our Pool School and see what we are all about. Pool School

Thanks,

Jim R.

 

[m_apple]

m,

You have the classic symptoms of having algae, even if you can't see it yet. Your filter is doing what it was designed to do..

My guess is that you are running your FC at 1 ppm or less and have almost no CYA in your pool... Any FC your cell makes is being quickly consumed.

You need to do what we call an Overnight Chlorine Loss Test or OCLT. Overnight Chlorine Loss Test

You should also take a good read through our Pool School and see what we are all about. Pool School

Thanks,

Jim R.

Thank Jim, will try this when I can and report back!

I use AquaCheck strips to test but will have to get a proper test kit to do an OCLT. The FC on the strips always looks to be around 2ppm or even 3ppm sometimes but that is likely because the SWG just keeps producing it. Your comment about CYA is correct - virtually 0. I recently added a bunch which brought it up to around 40-50 but noticed shortly after it looks like it's back at 0 and I couldn't figure out why. It never seems to have held the CYA but I never bothered worrying because the water has always been clear and the FC levels appeared where they needed to be... but this all makes total sense now if in fact it's an algae issue.

Thanks,
Michael

 

[SDor]

CYA doesn't really get used up. The only way to meaningfully lower your CYA is to replace water. Therefore, I'd say it's more likely your test strips are giving you unreliable results. As long as the pool is clear, I wouldn't change anything until you get your test kit and have accurate data to work with. Otherwise, you might just be chasing ghosts (like a 40-50 drop in CYA in a few days without replacing any water).

Also, depending on what falls into your pool, backwashing every week is really not that unusual (at least for me, going on 18 years of running my pool), especially in the spring where trees and flowers bloom, then die, then get blown by the wind into your pool and bits break apart and they fall through the skimmer and pump basket (at least this is what happens to me) . Tree pollen is also a big contributor. Also, if you have regular swimmers (or kids of an age who are probably peeing in the pool), that will also fill up the filter.

As an aside about kids peeing in the pool, all my kids and their friends swore they never peed in the pool, and would occasionally come in to use the bathroom, but the chlorine demand and filter backwash frequency told another story... I didn't realize it at the time, but since they got into high school and beyond, the chlorine use and backwashes required have really gone down...