Can't maintain Free Chlorine over 0.2...?!?

[rtilghman]

New pool, opened about 5 months ago. I've been balancing the chems regularly, cleaning it, and keeping everything in tip top shape. However no matter what I do I can't seem to get my Free Chlorine over 0.2. At first I thought maybe my test kit was old (Taylor K-2006), but when I shock the pool the Chlorine level is detectably high (bright pink), so that wasn't it.

• Pool - 15,500 gallons
• FC - 0.0
• CC - 0.2
• PH - 7.4
• ALK - 100
• CYA - 35 (approximate)

I'm in Austin, TX, which typically has a lot of sun (enemy of chlorine, though this spring has been particularly rainy and overcast. In terms of my kit, I have a tablet Chlorinator (Pentair 320), which most recently has been set to 3.5 (little over mid-point, which seems high) along with a UV filter (Trident series 2, no UV lectures please). I also have a Hayward variable speed pump (EcoStar SP3400VSP), which I run as follows:

• 8am - 10:15am - Full Speed (3450 RPM)
• 12pm - 5pm - Half speed (1725 RPM)

I'm simply baffled by the inability to maintain the chlorine level. The pool doesn't get dirty too quickly, but algae is forming way too easily and having to shock the pool regularly is annoying.

Would appreciate any help or insights.

Thanks,
Rick

 

[GuinnessPhish]

Sounds like you need to buy the TF 100, and do a proper SLAM.

 

[Richard320]

An Overnight Chlorine Loss Test will tell you if it's organics (read:algae) consuming your Chlorine or something else.

One thought is that the UV system might be downstream of the chlorinator. In which case, you add the stuff and then immediately destroy it with UV. Be sure to shut off the chlorinator and the UV during the OCLT no matter what, so they don't confuse things.

If you do lose FC overnight, you can rule out sunlight and the UV system, which means algae is starting to form. The cure is what we call the Shock Level And Maintain Process. A single megadose of chlorine - a poolstore "shock" might kill a bunch of algae, but it may not kill all of it. The Maintain part is the key. If you do have to go that route, I suggest ordering some refills for the FAS-DPD test now, because you'll be going through powder and drops at an alarming rate. Your test kit is one of the recommended one, so there's no excuse for delaying if a SLAM is called for.

 

[rtilghman]

The K-2006 is a pretty strong test kit, so not sure if I need the T100 instead/as well. As for SLAMing, I've shocked the pool multiple times with no problem... the pool comes out crystal clear, shocks just fine. The problem is MAINTAINING the chlorine level... it simply will not stay above 0.2 and I can't figure out why.

Interested if anyone knows a reason this might be. Do I just need to jack up the chlorinator setting? Should it typically need to be set to 4+ with light swimming in the spring in texas?

Thanks,
Rick

 

[ping]

There are only 2 things that consume chlorine; sunlight and organics.

To rule out sunlight consuming the chlorine you must perform an Overnight Chlorine Lost Test, OCLT. I suggest raising the FC level to 10 an hour before night time to run the test.

Organics do not have to be visible in the water to consume a lot of chlorine and that is my best guess on what is happening right now. If you want to eliminate organics, the SLAM PROCESS must be followed from start to finish or else the organics just multiply and you never solve the chlorine demand. Once the SLAM is complete you then need to follow the FC/CYA guidelines to prevent the algae from returning in the future. See my signature for all the links.

 

[jblizzle]

One thing that no one has pointed out is that exclusive use of trichlor tablets is not recommended ... especially where you do not close the pool in the winter.

Also, you get plenty of sun that provides the UV for free ... your use of a UV system is actually breaking down more of the chlorine you are trying to add. In TFP's opinion, UV and ozone systems serve no purpose in an outdoor residential pool.

Have you discovered Pool School yet? Start with these:
ABCs of Water Chemistry
Recommended Pool Chemicals
How to Chlorinate Your Pool

 

[rtilghman]

I guess someone missed my "no UV lectures please" line. However, if you must lecture about UV, note that sunlight UV doesn't penetrate anything but the first foot or so of water (making it mostly useless for a 6.5' deep pool like mine). The comment that UV filters do nothing is simplistic and inaccurate. UV filters DO do something, but how much is open to argument (since it depends on how much you run your filter).

Anyway, thanks for all the ideas folks. On the topic of SLAMing and OCLT, as I mentioned I've shocked the pool previously (always starting overnight), raising the level to around 12 (my CYA being about 30/35). Not saying a SLAM isn't called for, but my previous shocks haven't been underpowered (I used liquid pool grade bleach, 10% I think?) and entirely cleared the pool. Reading through the SLAMing page, it doesn't directly say this, but are you basically maintaining a 12 FC level until you see less than a 1 FC drop overnight? Adding in more shock constantly to maintain your level?

One other question is if I was losing a lot of chlorine to bacteria and algae wouldn't I see a higher CC level? My CC is only about 0.2 right now...

Thanks,
Rick

 

[jblizzle]

That was hardly a lecture ... simply pointing out one reason your FC keeps disappearing.

Yes, you should be maintaining the shock level FC until you pass the 3 criteria to stop.

CC do not always show up when fighting algae ... they are broken down the the FC, the sun, and your super-terrific UV system

 

[rtilghman]

Ha. Thanks!

On a sidenote, my UV system is forward of my chlorinator.

-rt

 

[jblizzle]

Right, but there is still FC / CC in the water passing through the UV system from the bulk of the water.

But, the UV system is not likely the major player here. There is likely something in the water.

You should SLAM and after that use bleach to keep adequate FC levels in the water (see FC/CYA Chart) if the chlorinator can not keep up. Very soon you are going to have to stop using it altogether.

 

[rtilghman]

Makes sense. The weird thing is just that the water is CRYSTAL clear after shocking about 5 days ago, even with some kids swimming this weekend. The only noticeable issue is some small algae in spots, but that only seems to happen when we see rain (which, oddly, we've seen a lot of lately here in Austin). Without the rain I never had any algae at all and the water was crystal clear, but the FC was STILL 0.5 at best.

Anyway, it sounds like my best bet is to SLAM it and see where I end up, so I'll get some more liquid chlorine this evening and plan to spend the next few days super shocking it. Hopefully it'll resolve the problem. I'll report back if it doesn't.

Thanks all.

rt

 

[jblizzle]

Sounds like you have been mostly lucky in the past, but that luck may soon run out.

Just follow the ShockLevelAndMAINTAIN Process and hopefully you pass the 3 criteria to stop pretty quickly since the water sounds clear.

 

[ewkearns]

I guess someone missed my "no UV lectures please" line. However, if you must lecture about UV, note that sunlight UV doesn't penetrate anything but the first foot or so of water (making it mostly useless for a 6.5' deep pool like mine). The comment that UV filters do nothing is simplistic and inaccurate. UV filters DO do something, but how much is open to argument (since it depends on how much you run your filter).

I won't even try to guess how much UV penetrates water, nor how effective UV filters are. However, I think you can expect to burn off about 3 ppm/day of chlorine.... just from the sun. From your post, I assume that is accomplished at or in less than the aforementioned 6.5' depth, since my pool is only a bit deeper and loses that amount.

Given what you have noted, the easiest explanation (Occam's Razor) is that your algae is consuming you chlorine at a rate faster than your are replacing it. IOW ((3 PPM/Day)+(The Algae's appetite)) > added Chlorine.

Short answer? Just SLAM.

 

[rtilghman]

Howdy folks. Thanks again for all the help and responses, wanted to circle back on this after having gone through the SLAM routine.

So, I spent about 5 days SLAMing my pool. Followed all the instructions, took the Chlorine up to about 14, maintained it there for the duration, and then let it drop naturally once it seemed like the Chlorine had stabilized, setting the chlorinator to about the mid-level (2.5).

However, a few weeks later I'm now having the following issues:

- The chlorine level is now back to zero
- But the pool is still crystal clear
- I'm now having a more visible algae problem, with algae on the shallow side of the pool (which gets the worst circulation)

I'm thinking I need to SLAM the pool again and spend some time brushing it to keep algae off the side. However, I have a couple of questions before I do this:

1) The Taylor instructions seem to differ from the SLAM guidelines on TFP... Taylor seems to say I should take the Chlorine to 30. Should I do that next time? Is there any danger with going ridiculously high on the Chlorine?

2) My pool is new, but it was a long build, and there was a period after inspection when the plumbing was open (not pressurized). Could a bunch of algae have formed inside my plumbing? Is this an issue? Will the SLAM address this?

3) I haven't cleaned my filter since the pool was opened. Pressure is good, but is it possible there's a bunch of algae in there? Will the SLAM address that?

Thanks in advance for any help. I'm fine with SLAMing again (kids will hate it), but I want to make sure this is the LAST time (at least for now).

Best,
Rick

 

[jblizzle]

How often were you testing the FC levels to make sure they did not drop? Almost sounds like you did not test for a few weeks.
And what is this "chlorinator" you speak of?

1) You should follow the ShockLevelAndMAINTAIN Process with the FC that is appropriate for youf CYA level (see the FC/CYA Chart).

2) The SLAM would have addressed this

3) You should clean the filter when the pressure rises 20-25% over the clean pressure. Although given the history, I would clean it.

If you do not want to SLAM after this, then you need to start testing and verifying adequate FC is in the water and if you keep using the trichlor tablets your CYA is rising requiring a higher FC level.

Please add your pool details to your signature as described HERE as it will help us help you.

Still liking that UV system? Does not seem to be helping much

 

[rtilghman]

How often were you testing the FC levels to make sure they did not drop? Almost sounds like you did not test for a few weeks.
And what is this "chlorinator" you speak of?

1) You should follow the ShockLevelAndMAINTAIN Process with the FC that is appropriate for youf CYA level (see the FC/CYA Chart).

2) The SLAM would have addressed this

3) You should clean the filter when the pressure rises 20-25% over the clean pressure. Although given the history, I would clean it.

If you do not want to SLAM after this, then you need to start testing and verifying adequate FC is in the water and if you keep using the trichlor tablets your CYA is rising requiring a higher FC level.

Please add your pool details to your signature as described HERE as it will help us help you.

Still liking that UV system? Does not seem to be helping much

I SLAMed and tested per the instructions in the page you linked, including ensuring the chlorine level was matched to my CYA. Basically I SLAM perfectly over a course of five days, at the end of which I wasn't seeing a drop in chlorine level in the morning. That said, maybe I missed something, who knows.

My question is really around the fact that the Taylor instructions seem to recommend 30ppm as the target, as opposed to the 14ppm recommended in the TFP SLAMing guide (based on my CYA level). I wondered if I should SLAM with a much higher chlorine level, if that would be more effective, and if there were any issues with having such a high chlorine level for 4-5 days.

Thanks for the insight about the pressure. My filter is about 33% of the way between the clean level, so maybe that's part of my problem. Either way I'm sure that cleaning it can't hurt.

On the chlorinator, see my earlier posts for pool/equipment specs. On the UV filter, yeah, I wouldn't expect the UV filter to be able to overcome an out of control algae problem... I would expect it to enable me to use a little less chlorine once I have the pool stabilized and clean.

Best,
Rick

 

[jblizzle]

Does the Taylor mention what CYA is assumed for the arbitrary 30ppm FC target? If not, I would ignore them.
I have never seen these instructions you speak of.

The SLAM method always works and is designed to not damage anything.