Milky blue water for 2 weeks despite SLAM, wondering if sand filter at fault

[canadianguy]

I’m really hoping that someone can help me diagnose what could be causing persistent milky blue water in my pool over the last 2 weeks, despite going through a SLAM type treatment. My hunch is that the sand filter may not be doing its job, but let me explain first what I have done so far.

I opened the pool 2 weeks ago to find it dark green with plenty of algae. I shocked it with 3 jugs (30 liters) of chlorine, ran the pump 24/7, and the green turned to a milky blue over 2-3 days. I added more liquid chlorine daily to keep the shock level high. I’ve had the pool for the last 10 years, and this sequence has been fairly normal, and in previous years the water has cleared up completely within a week. The algae was worse however this year than in previous years. I am generally fairly good at staying on top of the chemistry (carefully following all the advice in Pool School here at TFP!) and keeping all the chemicals in balance to ensure clear water. But this year has been a disaster: despite maintaining super high levels of chlorine for two weeks (and other chemical levels seem ok), the milky blue color just will not improve. I can’t even see the bottom of the shallow end. I have tested the water every day recently at a reputable pool store, and nothing seems out of whack. Here are the test results for today:

CC: 10.0 (the pool store uses a PalinTest 25 Photometer which maxes out at 10 for CC)
FC: 8.3
PH: 7.4
CYA: 20
TA: 70
CH: 141

I have brushed the pool floor several times, I have vacuumed it, and I have backwashed and rinsed the sand filter. When I brushed the steps in the pool at the weekend I could see clouds of dead algae coming up. In total, I must have used 12-14 jugs of chlorine over the last 2 weeks, which is 3-4 times more than I have used in previous years when opening the pool. Last night I turned off the pump to see if letting any particles settle at the bottom of the pool would improve clarity. No luck: the pool was the same milky blue this morning.

I did one thing differently this year: before opening the pool, I changed the sand in the sand filter as I wanted to check the laterals were not cracked. The sand filter is 8 years old. After removing all the sand, it turned out the laterals were fine so I put them back in. I then added 6 bags of filter sand (300 pounds) as per the manufacturer specification (the sand came from a pool store and is nepheline syenite from Unimin). When pouring in the new sand, some of it did accidentally go down the main stem tube, though I vacuumed it out by attaching a nozzle to a shopvac. When the pool pump is running, the pressure is within the normal range compared to the past (around 22 psi).

I am wondering whether there is something wrong with the sand filter or if I made a mistake when I changed the sand and reassembled it? It is possible that some of the sand that accidentally spilled down the main stem could have remained inside the laterals (despite my vacuum attempt). But would this really prevent the filter from functioning effectively? I read on one of the TFP threads that the sand may not be packed down.

Any suggestions on what could be causing the milky blue color and what to do about it would be very helpful. Thanks in advance.

 

[tim5055]

Welcome to TFP!!

There is no such thing as

going through a SLAM type treatment

You need to SLAM Process the pool following all the steps.

Not much credence is given to pool store testing around here. While you would think that a "professional" would be the best, unfortunately in most cases it is quite the opposite. Between employees who blindly trust the word of chemical sales representatives and high school kids working in the pool store for the summer you end up with poor results from their testing. But, what can you do?? We base our pool care system on accurate testing and only adding what the pool needs, when it needs it. To do that you need your own accurate test kit. Order a TF100 and at least include the XL option. That will give you what you need while you are clearing the pool, and probably enough reagents for a couple of years normal use.

While you wait for it to get delivered, you have a homework reading assignment. Start with ABCs of Water Chemistry and Turning Your Green Swamp Back into a Sparkling Oasis

 

[Swampwoman]

Hello and welcome. I see you're from Canada, which means you won't be able to get the TFT kit. You could instead get the Taylor k2006, which i believe is distributed through Lowry's, though pricer than in the states.

If you live near a border and have a US mailbox though, the TFTkit is the way to go.

As Tim suggested, you can't really slam correctly if you don't know for sure your CYA. But I suspect your problem is that you've not added, and maintained, an adequate amount of chlorine, and further, if the cc reading is remotely accurate, you are also fighting to break something down still. What tells me this is the lack of color change and clarity.

So lets say your cya is 20 per the pool store. For 22k gallons, it would take about 4 gallons of 8% bleach to add 12 ppm (going up a bit from 10 so that it never drops below 10.)

With such low cya you could easily be losing 30% or more a day just to sunlight alone, never mind the organics. Add in the organics and it would be completely reasonable to assume you'd use 2 gallons a day for at least the first week...that would have put you at 18 gallons by the end of week 1.

Which is why I say I suspect that because you don't have a test kit, you aren't actually maintaining to your slam level per the [fc/cya][/FC/cya] and therefore you're kind of stalled.

Every minute during a Slam that you're under slam level is a minute you're not actually "maintaining" the slam. This is why a good test kit that can read high FC and cya is so critical to a slam

Hopefully, you can get your hands on something so you're not flying blind

 

[canadianguy]

Thanks Tim and Swampwoman for your advice. I will find some way to get a proper test kit either here in Canada, or else across the border in the U.S., so I can be confident in testing the chemicals. In the meantime, I will increase the amount of chlorine I am adding to the pool.

 

[AquaBoy]

I recently went through this and found my CYA to be at zero once I tested. Threw some stabilizer into a filter sock and let it hang in front of the skimmer for a couple of days while filtering, squeezing often to make sure it was all gone after about 36 hours. Once my CYA went up to the 40-50 range I saw a dramatic difference in the chlorine sticking around and finally a couple of days later I came out and the pool was crystal clear. I also vacuumed a few times like you did and figured I had finally grabbed everything, but once the pool became clear I could see quite a bit more dead algae than I had expected, so I was obviously fighting that as well. Once you do your own testing and get a truly accurate read on the CYA, I'd get that up as quickly as possible and then you may end up seeing more algae than you initially figured. That may end up telling you the full story as to why the cloudiness has been hanging around. Very frustrating, but at least once you get the full story you will know it beforehand next year when opening it up again and can prevent the delay!

 

[canadianguy]

Thanks - you could be right as the early test results from the pool store showed low CYA readings. I didn't think that would affect the chlorine effectiveness as it was cloudy and rainy at the time, but now the sun has appeared so i agree that nailing an accurate CYA reading is important. I should be getting the LaMotte 7022 test kit early next week. Will post the results here as soon as I have them.

 

[canadianguy]

As an update, there has been virtually no change in the milky blue color of the water since I last posted. I have added approx 10 litres of liquid chlorine each day, brushed, vacuumed, and have kept the pump running continuously. I added a small amount of stabilizer to boost the CYA level. I also added DE over the weekend, which had no effect apart from raising the filter pressure by 1-2 psi. I just received the LaMotte kit today and have done my first test, which gives the following results:

FC 13.2
PH 7.0
TA 100
CH 280
CYA 20

Based on the Chlorine/CYA chart, my chlorine seems to be at SLAM level, and I suspect it has probably been at SLAM level for some time given the amount of chlorine I have added on a daily basis over the last three weeks. So my question is why haven't I seen any improvement in water clarity? I still can't see the deep end of the pool. It hasn't exactly been hot or sunny here in southern Ontario recently, so it's unlikely the chlorine has been burning off rapidly. Plus, my daily visits to the pool store for water testing have always given a chlorine reading of 10, which is the highest level in their test machine.

I am really at a loss to understand what is causing the problem, and what to do about it. I know floc is a last resort but I feel I am running out of options, and am tempted to try it. I am also wondering again whether there could be a filter issue, though the sand filter has new sand this season (of the proper type for sand filters).

Suggestions, please!!

 

[Suziqzer]

You really should be testing and adding chlorine several times a day if possible, not just daily if you want the faster results. It's also hard to really know what you were doing with things without having an accurate test kit yourself. Pool stores are notoriously unreliable as far as testing goes.

I have also found that the milky blue seems to be the part that hangs around the longest. Just be diligent and keep trucking on with your SLAM process and you will get there.

 

[PAGirl]

My SLAM had seemed to stall, so I decided to open my filter. My sand was below the minimum. I filled it up and am now seeing some improvement.

 

[canadianguy]

So things have taken an unexpected but welcome turn for the better. I was out of the country for 10 days, and 2 days into the trip my wife told me that the pump had seized up. Not something she could easily fix, so I resigned myself to returning to a green pool with blossoming algae. Amazingly though, my wife texted me a few days later to say that the water had actually almost completely cleared up and she could see the bottom of the deep end for the first time this year. For a whole week the pump was off, the water wasn't circulating, and the weather was hot - and yet the water clarity dramatically improved. No more milky blue water.

So my conclusion is that the chlorine levels were fine (they had been above SLAM level for a while); the problem in fact was with the sand filter, which wasn't capturing micro particles or dead algae suspended in the water. With the pump not running, all the fine particles just sank to the bottom of the pool. When I returned from my trip, I fixed the pump and vacuumed to waste, which has largely sorted out the problem. The water clarity is currently not perfect but it is vastly improved from the milky blue state of several weeks ago which never showed any sign of improving.

I am puzzled about why the sand filter didn't pick up all the dead algae in the water, especially as I checked the laterals and put in new sand this year. Has anyone else had this problem? I will try adding another cup of DE but it didn't make any difference last time I did this. I'll check out the sand level within the filter too just to be sure it is not below the minimum (though I put in the correct amount back in May before opening the pool).

 

[PAGirl]

Are you keeping your FC at SLAM level still? I'd do an OCLT once the cloudiness is completely gone, if I were you to make sure you got everything.