Big Pool, Small Problem - Cloudy with balanced water. tips?

[stlcard87]

Hey guys new to the forum and in need of some help,

So ive just recently inherited responsibilities with pool chemicals and upkeep at work. For legal issues i cant say where, but our pool is 360,000 Gal. And is used by ALOT of people 7 days a week. By alot i mean an easy 300+ throughout the day. 530a-9p.

Im familiar with water balance, shocking and such. I come to you guys in need of some quick help/advice though. I have been struggling with cloudy issues for the past couple weeks. Heres a quick review of the water balance (It has been balanced for past 2 weeks, just recently got a little out of wack).

Taylor Test drops:

FC-5ppm
pH-7.2
ALK- 60ppm
CH- 250ppm
CYA- 80ppm
TEMP-87 - Direct sun all day.

Pool stats again:
360,000Gal
63 Sq Ft. Filter space (AKA 9 Large Sand filters)

As stated above Ive had clarity issues (looking for that crystal clear blue) I havent had issues in the past until this recent onslaught of new members this summer. If im correct, my water balance is not really the issue (waiting on the CYA to drop, one of my Lifeguards is a dummy)

I believe the issue is our filters. They and the sand have not been replaced in 25 years. Not sure if the sand has been chemically cleaned in past few years or what. No broken laterals that i know of. Ive tried Clarifiers, Non- Chlorine Shock treatments, Cal-Hypo Shock treat, and Flocs with little luck. Over the past week it has slowly cleared a little, but i feel it should be better.

Today i tried the DE in sand filter trick to see if it helps tomorrow morning. Pressure is slowly rising.

My question:
-Is my water balanced based on the amount of water/direct sunlight and number of guests per day?
-Could my sand filters be channeled?
-Should i Try a sand scrubber?
and are there any other tricks i can try out?

Im hopeful the DE will help.

Thanks in advance. sorry for the lengthy chatter.

 

[257WbyMag]

Welcome to TFP!

Although I have no experience with commercial pools such as yours, I will say that your CYA to FC ratio is a likely problem here. With a CYA of 80, the absolute minimum on your FC should be 6. The target would be around 9. With the swimmer load that you have, that low FC makes it tough when it comes to breaking down all of the swimmer waste, tanning oils, and sunblock. All of those things tend to make it cloudy, especially the oily stuff.

Redistributing the sand in the filters cannot be a bad idea at all, especially if you cannot recall of it having been done before.

 

[dmanb2b]

If this was a residential pool, I would say since your CYA is 80, 5ppm FC is a little low. FC of 6 is your min and you want to target an FC of 9ppm. Your PH is a tad low too. What is your cc reading?

By the way the above guidance is meant for residential pools, so just make sure you are following applicable laws regarding public pool maintenace, regardless of my opinion.

 

[duraleigh]

Welcome to the forum. :lol:

How do you chlorinate the pool? Have you attempted to shock up to around 25ppm to combat the cloudiness? When was the last time the pool was shocked? Has the FC been below 3-4ppm for any length of time?

 

[JasonLion]

With a very high bather load and high CYA level you need some additional oxidization beyond what chlorine can provide. The obvious candidates are UV, ozone, and MPS. With high CYA levels, chlorine alone just isn't going to keep up with that kind of bather load.

 

[stlcard87]

thanks for the tips, i might try poping the tops on the filters to make sure the sand is distributed properly. if the DE does not help clear up in a couple days. Im sure ill have to backwash soon.

Can you guys clarify with me the CYA : FC ratio? Ive seen the pages in the pool school, but im having trouble getting the big picture. I understand that with higher CYA levels it takes longer for the FC to "oxidize" the wastes and eliminate them. (correct me if im wrong...) which is why a higher FC level is needed?

I guess what im saying is why not just leave the CYA and FC alone till the CYA drops to a lower level that matches our FC level? or from another perspective, why do you say i need raise the FC more?

In the past we have kept our FC at 5 and CYA around 40ish (i think). Weve had good results in the past by keeping our santizer slightly higher than a res pool. (water balance is same for commerical as res with slighty higher Santizer levels.) The only difference is while you guys dump in a pound or 2 Im dropping 50 in. ha. (glad the funds does not come from my wallet) =)

CC= 0

Our Ph and Sanitizer is monitored by an auto feeder. Accutab- cholrine feeder (if you guys are familiar with that).

- duraleigh-
Last time we did a super shock, was to combat the beginnings of a mustard algae attack. Dropped a 50lb Cal-Hypo shock treat (for our 360,000 gal pool) (via the recommendation of our chem supplier) However, it never fully cleared again. This is the cloudiness i have been battling for 2ish weeks. I'm Assuming whats left in the haziness is dead algae and oxidized waste, thus I'm beginning to think its a filtration issue?

 

[duraleigh]

Hey,

Well, it is certainly above my paygrade to pontificate on manging a large pool but water is water and algae is algae, etc, etc.

I'll let others address the FC/CYA relationship.

Often on this forum and others, I see folks suspecting a filter problem when it's a water problem. I don't think you finished the shock process.

I could certainly be wrong but the cheap experiment is to run the FC up to around 24 and then, unlike the previous shock, hold that FC at that level as long as the swim schedule will permit. If the schedule will not allow you to hold your FC @ 24 or so for at least 24 hours (or preferably until it clears), then I believe you could accomplish the same goal by elevating your FC to around 8ppm and then holding it there 24/7 until the water clears. That may take several days but it costs little more than a few ppm's of chlorine and the end result may be a crystal clear pool.

 

[Richard320]

I guess what im saying is why not just leave the CYA and FC alone till the CYA drops to a lower level that matches our FC level? or from another perspective, why do you say i need raise the FC more?

CYA doesn't dissipate like Chlorine. It will only go away with splashout and backwashing. Or draining. Consider it a fixed value, and adjust the rest to fit it.

Long as you have the test kit out, what's CC? With the load you have, I bet it's high.

What time does the pool close? If it's something like 10 PM, push a hand truck with cases of Chlorine out around 9. Then start adding them, slowly. With a pool that big, a gallon of bleach is equal to a drop in a bucket! But it will clear the pool, I'll bet. Soon as it's empty, let 'er rip!

Or if it's empty at some point, start shocking then. If anyone shows up, say something like, "It's safe to swim in, but we had a little accident earlier, so I want to be sure it's totally sanitized." That ought to dissuade anyone from interrupting the process. }:>

 

[PaulR]

Can you guys clarify with me the CYA : FC ratio? Ive seen the pages in the pool school, but im having trouble getting the big picture. I understand that with higher CYA levels it takes longer for the FC to "oxidize" the wastes and eliminate them. (correct me if im wrong...) which is why a higher FC level is needed?

I don't claim to have a deep understanding, but I'll take a crack at this.... (I'm overdue for a good humbling. )

When you have CYA in the water, the "free" chlorine can either be bound to the CYA, or it can be an active sanitizer/oxidizer. There's a chemical equilibrium between these two forms, so as the active sanitizer gets used up, some of the chlorine bound to CYA gets released.

So, if CYA is higher but FC is the same, it's not that the FC takes longer to work, but that less of it is active sanitizer, because the equilibrium is tilted more toward the bound-to-CYA form. Less sanitizer = slower sanitizing. If your CYA goes up, you also need to bring up your FC, just to maintain the same proportion of active sanitizer.

This is why people are saying to boost up your FC level; this will tilt the balance more toward the active sanitizer side, and combat whatever is clouding the water.

I guess what im saying is why not just leave the CYA and FC alone till the CYA drops to a lower level that matches our FC level? or from another perspective, why do you say i need raise the FC more?

Because CYA pretty much doesn't drop by itself. If you pump water out (e.g. for backwashing) and replace with fresh, then you lower CYA because there was some in the water you pumped out and not any in the fresh. But to lower CYA by half, you need to replace half the original water. Obviously not going to happen in your pool anytime soon.
--paulr

 

[Isaac-1]

Again I am no expert on big commercial pools....

Just remember if your using tri-chlor based "stabilized" pucks for chlorination you are adding both chlorine and CYA in the process, if you instead use Cal-Hypo based you will add chlorine and calcium at the same time, and if you use liquid chlorine you will be adding chlorine and salt.

Looking at your numbers it seems your CYA value is very high, if you do not swap out about 30-50% of your water it will take a very long time for these values to fall on their own, mostly through splash out, water replacement (rain or intentional), there are other processes consume CYA, but it is usually a very slow process. As an alternative to water replacements there are commercial Reverse Osmosis services in some areas that can filter out CYA and just about anything else that is in the water.

You Calcium Hardness is about ideal now, still you might want to consider switching to a Cal-Hypo tablet until you get things under control

Of course your best bet may be to switch to manual liquid chlorination (at least partly) to keep your CH and CYA levels from getting worse.

It sounds to me like you are looking for a quick fix, if the problem is you have not finished the shocking process or can't maintain high enough FC levels due to the high CYA levels, then your only fast option that does not involve installing large UV, Ozone, etc. oxidizer system is to shock with MPS (Monopersulfate). It has the advantage of breaking down fast, so it is likely you could shock overnight while the pool is closed.

I also suspect the sand is a problem, sand filters work by catching dirt, over time the sand gets worn down and stops having sharp edges, you might be able to use the DE trick to help them for now, but I think you should seriously look at replacement of the sand..

Ike

 

[stlcard87]

Thanks for the help guys,

The DE trick is working slowly.

We do use a Cal-Hypo Tablet feeder.

Im about to go check the balance again, and if the FC isnt in the correct ratio with our CYA then ill adjust it so it will balance out. pH has also been adjusted back to 7.4.

Hopefully the DE will keep working once its cleared up i plan to pop the tops on the filters to check the sand/redistribute it with the garden hose trick.

Just out of curiosity. How many pounds of Cal-Hypo do you guys recommend we should use for a shock treatment? Pool is 360,000.

 

[stlcard87]

DE Worked some. Thanks for the Tips.

We ended up poping the tops to the filters and stirring the sand up with a freshwater garden hose, while simultaneously vaccuuming out the garbage. Turns out, the sand/ sunscreen/ hair/ and other nasty unspeakable things had compacted so firm that the backwash water pressure could not push the sediment up on its own while we backwashed in the past.

Stirred up all the sand, and cleaned them out. Worked like a charm! Im sure running a sand scrubber through the system wont hurt either, that is, once weve loosened up the other filters.

Thanks for the tips and help with water balance and such. Great site!

 

[PaulR]

Excellent work on clearing up the sand.

I plugged your numbers into the Pool Calculator (pH 7.4, TA 60, CH 250, CYA 80, temp 87) and it looks like it's still not quite what I'd call well balanced; I'd say bring up the TA to 80. At that point you have some headroom on pH and CH, without running into either corrosion or scaling issues.

Just for fun I checked out what 360K gallons requires in terms of bleach... raising FC by 1ppm requires 4 big jugs of regular bleach, or 2.8 gallons of 12.5% liquid chlorine. Less than I would have guessed! If you're losing 2ppm per day, that's maybe 40 gallons a week of the 12.5%. If there's a bleach supplier anywhere in your area, that would be worth checking out.
--paulr