Hayward sand filter blotches of crud on bottom of pool

[Putcheen]

Hi, I am new to this forum and joined because it looks like a good one. I inherited a 24' round pool when I bought this house 3 years ago. It has a Hayward S210T sand filter with a Vari Flo 711 Multivalve on top, all Hayward product. The first year I discovered (while changing the sand) that the center pipe on the Lateral Assembly was badly corroded (and was finding some sand in the pool). I also found it's OD [outer diameter] was exactly the same as 1 1/2 inch PVC pipe. I cut a piece of PVC to size and replaced the center pipe and it fit very well. It was a ***** getting out the broken pieces of the old pipe from the base as they were glued in. It seems to be working just fine so I post this to help out anyone finding their center pipe corroded because you have to buy the complete Lateral Assembly to replace just that center pipe (not sold separately). If anyone knows why or if what I did was a big no-no please comment.
I am having a problem with keeping the bottom of the pool clean from what looks like dead algae while running the filter. I treated the water and it all checks out well chemically. If I vacuum the pool to waste and then turn off the filter the water is clear and the bottom stays clean for a long time. I have to run the filter eventually though and when I do the pool will pretty quickly start blotching up on the bottom with patches of dusty crud. I have done backwashing after vacuum and seen all the crappy colored water exiting the filter. So should I replace all the sand again, it's only 3 years old? I've read that sand shouldn't be replaced too often. I've read to put some DE on top of the sand and then vacuum and backwash. Anyway, I'll probably replace the sand again and clean out the filter tank as best I can and .. I don't know.. something else?
Any experienced comments would be appreciated. Thanks.

 

[duraleigh]

WElcome to the forum! :lol:

I suspect your problem is in your chemistry rather than the filter. It sounds like you are accumulating dead algae on the pool floor and when you turn on the pump, it is being gathered into clumps.

Posting a complete set of test results will help us determine the issue but it doesn't sound like it's the filter.

 

[Putcheen]

Thanks so much for answering. I use standard test strips and a 4-way test kit (5 drop solution bottles) to test my water. The test strips are a puzzle to read (a little) because the top and bottom are not showing a solid color but a faded shade or tint of a color so I estimate the closest shade/color. If I'm reading them correctly from top to bottom:
the pH = about 7.8 or 8.0
the FREE CHLORINE = above 10 maybe 15
(I opened the pool last week and have it super shocked/chlorinated since that day)
TOTAL ALKALINITY ppm = around 120
STABILIZER = around 100

Using the kit with the drop solutions: Chlorine = bright yellow (10 to 15?)
pH = between 7.4 and 7.6 (closer to 7.4)
Acid Demand = 3 drops ( I have appr. 13000 gals in pool)
Total Alkalinity = 20 drops to make solution clear = 200ppm

By my interpretation I need to add between a pint or two of Muriatic Acid to make it all good. But I'm by no means an expert.
More Info::
My water here is from the garden hose and it's well water and pretty hard too. It requires a water softener in the home and a whole house filter. I also use another filter for drinking water. I live next to a small forest preserve if that matters. Any algae in that pool will have to be chlorine proof to be alive so I'm pretty sure the particulate on the bottom is dead algae (not to mention that a pool guy came by the house right after I bought it, inspected everything and told me so). There is never anything on the walls of the pool only the crevasses and folds on the bottom of the lining. It is like a powder that will fly away when you disturb the water around it. It's like a dark brown/blackish color. I get full sun all day. The particulate settles in the full sun and where there's shadow (there is shadow only late in the day) with no preference. The water is clear not cloudy. After I vacuum to waste it will not show at all until I start the filter again ( I've kept if off up to 2 days and no patches showing). I was told that new sand will not trap any particle smaller than 50 microns ( 20 - 25 if sand is "dirty") and that dead algae can be as small as 3 microns. I imagine buying a new cartridge or DE filter would cure or disprove the "dead algae" idea but I'm not going do that. I've never used a cleaner for the sand yet. I've never used an amount of DE on top of the sand. I've never tried Zeolite, it's expensive. That's it.

 

[duraleigh]

I am reluctant to tell you it is the filter's fault. There are hundreds, perhaps thousands, of sand filters on this forum (mine included) that have no problem filtering dead algae from a pool.

So.....

1. When you see the dirty water coming from the returns after backwashing, have you used the "rinse" position for at least 60 seconds or so?

2. What level do you normally keep your chlorine when you are not shocking?

 

[Putcheen]

That is a good point. I had been neglecting the "Rinse" cycle the first 2 times and only the last 2 times have I used it. I will keep the same sand for while (maybe) and try several vacuum/backwash/rinse cycles over the next week to see if it makes a difference. Someone (my neighbor) suggested a "floc" agent to clump the small particles. I don't know but I've heard it said you shouldn't backwash unless your pressure is up around 15 psi on the gauge but I need to do it every time I vacuum which is at least twice a week.
After the "shock" treatment is over I think I need to maintain the Free Chlorine at around 3 to 5 ppm.
thanx

 

[duraleigh]

After the "shock" treatment is over I think I need to maintain the Free Chlorine at around 3 to 5 ppm.

If your CYA is at or around 100, that is not enough to prevent algae from forming.

With your CYA that high (You should get a good test kit so you can confirm that), YOur FC should be somewhere between 5-10ppm and never below 5ppm for any period of time.

I cannot say this as a fact, but I still suspect what you are seeing on the pool floor is dead algae but it is coming from live algae still in the pool. Your low level of FC is killing some of it but not enough to kill it off completely so you are constantly seeing it appearing on the floor.

 

[ivyleager]

Yes, what he said.

With a CYA of 100, you need to keep your FC up to 8-10. I had to do this my 2nd year of pool ownership. Too many pucks and use of granular chlorine to shock. I am on a well and did not want to dump water, so I just maintained high chlorine levels until I opened the next spring. CYA had gone down to 65. More manageable.

Also, what is your filter run time?

 

[poolbljn]

I have had same problem in my pool since switching from a cartridge filter to a sand filter. Even right after the filter was new - within a month I was seeing this at the bottom of my pool. Vacuum and it looks great for a short time but comes right back - it is getting worse. I am considering going back to a cartridge filter to see if I can prove it is the sand filter. If you find a solution please post. I don't really know what to do next

 

[Putcheen]

Thanks for the good input. I ran the filter 24/7 for the first 3 or 4 days after the initial shock and that cleared up any cloudiness I had at first. After the settling dust/dead algae problem started I shut the filter off for 2 days after vacuuming to waste (water bill!) and the pool stayed clear. I tested everyday though. I started the filter again just on circulation for 2 days for about 4 hours a day and then have been running the filter from 4 to 8 hours a day. So I gather that CYA = Stabilizer? I didn't know that I wondered what it meant. Mine is high? According to the test strip it reads in the OK level. I suppose I have to go buy Stabilizer at the pool store. What kind of test kit is considered "good", is price the only measure? I just thought any kit sold in stores would be fine and looking online some look like junior chemistry sets and are priced pretty high.
I'll post later in the week any results of vacuuming (not to waste) and backwash/rinse cycle and if it leads to reduced amounts of dust. I will keep my FC up around 10 (purple on the strips) til then.

 

[duraleigh]

I suppose I have to go buy Stabilizer at the pool store.

No, It's too high already. Don't put in any more.

I'll let others advise you on which kit to purchase (I make one) but trying to use test strips is a losing battle.