FC PPM Levels

[Switched]

So I’ve had my pool for a year now and never had a pool before.
I’ve had a couple of instances of cloudy water previously that I’ve needed to do a SLAM and got it looking good but I’ve come to realise there is a few things I’ve changed recently to help it be crystal clear.
1) I never actually scrubbed the pool walls ever in a year. I now scrub it once a week
2) in summer as my temps rose, Iwas only running pump for 6 hours, now I am 9 hours after needing to SLAM on the last bout of cloudy water. 6 hours was enough to turn over water once a day.
3) I have heavy leaf and pollen drop and would leave my pool cover for days without cleaning it up, so now I do it every two days or so.
4) I try and run my robot twice a week, from previously once a week.

I don’t know which point above has helped me the most to keep it looking crystal clear?

Previously I did noticed that always the entrance to the pool that the tiles were slippery, but didn’t think too much as the tiles were tiled on a curve. It was a post where I read that slippery tiles means algae is starting and to brush it ASAP. Since doing so the slipperyness is I think all gone. I must be honest and assumed that my robot maytronics m400 meant I didn’t have to hand scrub so I never did it until 3 weeks ago. I actually had two periods of cloudy water previously not long after each other and always maintained a CH of around 6ish as my baseline but one morning I woke and tested and CH was at zero!
So I’ve learnt my ways and I think I’m now on the right track with the new steps in taking.

here’s my question then. When I read about what levels CH should be, online a lot of resources say 2-3ppm. I know the TFP way and follow that but I wonder about the online methodology. I feel this is too close to 0, and it’s likely if you are not checking everyday at some point you will end up at 0 which isn’t good.
I know to use the cya to CH chart and do it religiously but why are a lot of resources saying 2-3ppm as it would be quite difficult to keep at this level without it ever hitting 0.
How long can a pool be at 0 CH and not have algae?
I find myself targeting around 6-8ppm now based on my CYA level so to avoid a SLAM, but sometime it can get to 9 or 10ppm

 

[JJ_Tex]

Proper chlorine levels is the most important factor, but I'm sure brushing helped as well especially brushing any areas that your robot cannot reach like stairs, tanning ledges, etc.

As for your questions on chlorine levels, as you know TFP recommends the FC level based on your CYA. The FC/CYA relationship is newer thinking, and the pool industry is slow to adopt. As you see, many places just use a blanket recommendation for FC between 2-3 with no regards to your CYA.

There is also no set timeline as to when you will get algae when you fall below the minimum FC. It depends on lots of factors like the contaminants in your pool, water temp, etc.

 

[Jimrahbe]

Switched,

I have a saltwater pool and here is what I do...

I try to always maintain my "Target" FC or higher... I never try to keep my FC between the minimum and my Target.. I treat my minimum as a cliff that I never want to fall off.

Running your FC above your target will not hurt anything... It does waste a little chlorine, but I personally think it is worth the small cost..

Ref this chart.. FC/CYA Levels

Thanks,

Jim R.

 

[CrystalRiver]

2-3 FC is really, really low. Even without CYA factoring in, drinking water can be up to 4 ppm. I certainly don't want to take a bath with others (and their germs), which is what you are doing when swimming in a body of water with FC that low.

The 1-3 ppm FC was established before CYA was a thing. Now, we all use CYA, but the laws have not caught up. Science says, with more CYA, you have less effective chlorine. You also lose less chlorine to UV, which is the benefit of CYA. Before, you could dose the pool, and essentially all chlorine was gone within an hour or two, because the sun burned it off. Now, with CYA, chlorine will stick around for days. But, trade-off is, you need a bit more chlorine in the water for the same effectiveness. It's not much of a trade-off, really, as the chlorine is buffered by CYA, making it less harsh on eyes and bathing suits at the same time. What it really does is provide a larger reserve of chlorine before you hit effective zero, the point where it cannot do its job to sanitize the pool.

Water with 0 FC will have algae. Period. The spores are in the air and constantly falling into the pool. It's impossible to see until it's grown a LOT, so you might not see it, but it's there. Algae is slimy and not pleasant to look at, but won't hurt you. Of much greater concern are pathogens, which start growing before algae can survive.

 

[Switched]

Thanks everyone for the responses. Thinking it about some more I may back off my pool pump by 1 hour and see how things go with the water. Of course I want to maintain the quality of the water with as minimum run time of the pump - electricity is expensive in AUS.

one other question - do people prefer to test water in the morning or evening.
Interestingly if there is something in the pool consuming chlorine then I assume it’s eating chlorine overnight and it’s better to see minimum FC levels which means morning it would be before to test before SWG starts?

 

[CrystalRiver]

Some people run their pumps primarily at night due to lower electricity prices at night. Some run primarily during the day to run solar heat or water features. Pick whatever time works best for you.

If there's nothing in the water consuming the chlorine, and SWCG does not run overnight, then your levels should be identical at sundown and sunrise. UV (sunlight) and organics (algae, bather waste) are what consume chlorine.

 

[mgtfp]

When I read about what levels CH should be, online a lot of resources say 2-3ppm

Unfortunately, the pool industry never bothered to understand the chemistry of CYA. They understand that CYA protects chlorine from UV by business building a chlorinated CYA-molecule that is a lot more resistant to UV (still not 100%).

The question that arises (and that you would expect pool professionals to ask themselves) is: If chlorine is building a relatively strong bond with CYA, is it actually still effective as a sanitizer and oxidizer?

The answer is NO.

The chemistry has been described in 1974 by a guy called O'Brien. It is available here on the forum via the search for those interested in chemistry.

Simplified in a nutshell: Between CYA and chlorine is an equilibrium reaction going on, where the vast majority of the chlorine is in a bond with CYA, and only a small fraction remains "active" chlorine (chemically: HOCl). This active chlorine does all the sanitation, killing algae, oxidizing sweat, etc. In doing so, the active chlorine is turned into salt (Cl^-). That means the equilibrium between chlorinated CYA and HOCl is disturbed, and some chlorine gets released from CYA to become active chlorine (pretty much immediately). You can therefore think of the chlorinated CYA as "reservoir" chlorine.

This equilibrium also keeps working in your FC test: The changing colours in the test basically inactivates the active chlorine, more chlorine gets released from the "reservoir", gets inactivated by the test chemicals, and so on until all the reservoir chlorine eventually shows up in the test (all of this is happening within fractions of a second).

Therefore all of the active and reservoir chlorine together test as "free" chlorine (FC). But "free" doesn't mean active. "Free" is just used to differentiate from "combined" chlorine (CC), which is an intermediate product in the oxidization process of things like sweat or urine.

That's the misunderstanding in the pool industry: They work on the principle FC = AC (I just call active chlorine AC for now, that's just me, not an official abbreviation).

Ideal would be to test directly for AC. But that is not really possible in a residential pool setting. The next best thing is what TFP is doing. Test for FC and CYA, and then calculate AC based on above mentioned O'Brien paper. That's the basis for TFP's FC/CYA-chart.

The takeaway message is that the FC/CYA ratio needs to remain about constant to keep the active chlorine amount constant. If you double your CYA, you also have to double your FC to keep your pool in shape.

That also means that it is perfectly safe to maintain higher FC levels following the FC/CYA-chart. The reservoir chlorine is not aggressive to swimmers or pool equipment.

In fact, 3ppm FC without CYA is far more aggressive than our SLAM-level FC. If you wanted to maintain a pool without CYA, you actually needed to maintain an FC of something like 0.6ppm. That's incredibly difficult as you constantly have to replenish chlorine lost to UV and bather-load without overshooting. Not impossible, but challenging and not cheap. This is for example how things have to be done in public pools in Germany.

But it is far easier and economical, especially in a residential pool setting, to add CYA and increase FC according to the FC/CYA-chart to have a nice, non-aggressive (moderated), chlorine reservoir. TFP even recommends a small amount of CYA in indoor pools (where you don't have losses due to UV), just for the reservoir effect.

Next time, a pool professional goes crazy seeing your 6 or 8ppm with CYA, ask him if he'd be concerned about 3ppm without CYA - that's where I'd be concerned, as it is just unpleasant to swim in such water. Unfortunately that's what most indoor public pools do, and why you smell like chlorine even after showering, and why your swimsuits disintegrate so quickly in public pools.

 

[mgtfp]

one other question - do people prefer to test water in the morning or evening.
Interestingly if there is something in the pool consuming chlorine then I assume it’s eating chlorine overnight and it’s better to see minimum FC levels which means morning it would be before to test before SWG starts?

The main problem (for me) with regularly testing in the morning is that it's just not on my radar when I'm busy making school lunches, breakfast etc.

I run my pump for about 10h with some breaks throughout the day to keep the surface skimmed (I get a lot of leaves) and adjust my SWG to end up with the right amount of chlorine at the end of the day.

Then, usually after dinner and definitely after my pump has stopped for the day, I run my tests. I know my system well enough by now to know how much chlorine loss to expect depending on cloud coverage and bather-load, and I know how much chlorine my SWG is producing. If something doesn't add up, this evening test will give me an immediate base line to run a proper OCLT over night by testing again first thing in the morning.

A nice side effect of running the pump throughout the day is that by producing the chlorine as it's being used, my chlorine remains pretty much constant throughout the day. It usually doesn't matter too much when I test my FC. If the evening result is the same as the day before (i.e. I was producing as much chlorine as was lost), then the chlorine remains constant throughout the day by about +/- 0.5ppm. Therefore, it's usually not a big deal if one day I can't run the test in the evening and test in the afternoon instead.