Have I got green algae?

[SingingSailor]

It seems I've gotten some algae problems for the first time, and could use some help from people with experience.

There's a greenish "powder" all over the bottom and lower sides of the pool. It is easy to scrub away, making clouds in the water, and the filter cartridge becomes dark green. When it was at its worst, free chlorine dropped to 0, with Total Cl of about 2. The pool sides are though not slippery. I guess this is green algae?

I treated by shocking with 0,4 litres of dichlor, which should give about 13ppm in my 17.000 litre pool. This stopped the algae growth, and I thought everything was ok. Today, 5 day after the shock treatment, the free Cl is still at about 8-10ppm (!), and algae seems to start growing again. Can algae grow at that level of Cl, and if there is algae wouldn't the Cl level drop more quickly? It is possible that I have a high CYA level though.

Test results:
pH: 7,2 - 7,4 (phenol red tablets)
Alk: 50 - 150 (test strips....)
CYA: 0 (test strips... )
Free Cl: 8-10ppm (DPD tablets, measured mixture of 1 part pool water and 3 parts tap water, DPD reading is about 2,5ppm)
Tot Cl: Not measured recently.

The CYA level could be high: I´ve used about 2 - 4kg in total of trichlor and dichlor this season, which should give 60-120 ppm CYA in my 17000 litres (if I calculated correctly). But the test strip shows nothing... I've been trying to measure CYA with strips since I bought the pool four years ago, but never got them to show anything. I've always thought that since I change water every season I never used enough tri/dichlorine in one year to make a difference, but now after trying to calculate the added CYA I´m not so sure.
This year I started using dichlor for shocking, partly because I got it very cheap, and partly to try to get some CYA in the pool. Now I have algae for the first time, maybe not a coincidence...

Anybody had experience of test strips showing zero CYA when there actually is a high level of CYA?

Finally, anybody knows how to get a good test kit in Sweden? They don´t ship the TF-100 to Sweden...
My alternatives for CYA measuring is my Aquacheck strips (seems not working) or the LaMotte ColorQ, which is very expensive and still not very reliable?

 

[Patrick_B]

Yes, there have been many people getting false low readings on CYA from strips. They are notoriously bad. As for getting a good kit in Sweden I'm not sure what to do. I know you can't get the TF-100 shipped in...or almost certain you cannot. There has to be a FAS-DPD Cl kit at the ready over there I would think however.

Algae could absolutely be growing at the level of Cl you mention especially with a high CYA level, which in your case seems very likely. It would really be helpful if you could get an accurate reading for CYA because without it, you are guessing at how much Cl you actually need. Looks like you need a lot more, and I would suggest that you use bleach/liquid chlorine, and not Di or Tri Chlor until you have a handle on the CYA level. I'm not sure what you have access too over there, but surely you can get straight 6% bleach eh?

Hope this helps, and welcome to TFP by the way.

 

[frogabog]

I am going to point out that shocking the pool isn't a one time event of dumping in shock product and nothing more (as you described your recent shocking episode), but rather a process that involves maintaining shock level (test & replace chlorine hourly at first) till the three criteria are passed.

1) <.5ppm CC
2) 1ppm or less chlorine loss overnight (OCLT)
3) water is clear

I think the root cause of your current issues are not shocking as described in pool school. I suggest you read through it, paying particular attention to the shocking and algae sections and plan to shock your pool again. It will likely take a day or more to pass all three criteria but once you do, you won't see algae growing at normal chlorine levels.

FWIW, I felt the need for a laugh today so I stuck a strip into my pool after testing with FAS-DPD at 4.5ppm, PH-7.2, TA-80, CH-20, and a known CYA level of at least 40ppm. Test strip showed 0 chlorine and less than 0 CYA if that's possible (pad was several shades lighter than the lightest shade on the box), TA 120, CH 100, PH 6.4... wow... If I adjusted my pool according to that it would most certainly be out of control with a quickness.

I'm also a little more than ticked about the PH so low due to the two 3" trichlor pucks I used this week. No wonder we always had to mess with ph those seasons we used pucks. PH was 7.5 on it's way down (for some reason my ph drifts down instead of up) when I put them in. Another confirmation pucks are not the best choice IMO.

 

[SingingSailor]

Thx for your replies.

For shocking, I can go back to using cal-hypo. Bleach is expensive and in low concentration over here.

I knew strips were bad, but not THAT bad. Thought I at least could see if there were some CYA or not.
I use them as a cheap indicator of presence of FC, but I find them useless for pH testing.

I've read the pool school, its very good and I´ve learned a lot from it.
The three criterias for shocking is surely very good, but impossible for me to follow all the way. I simply have no means of measuring CC when the FC is high (I use DPD 1 and DPD 3 tablets), and I can't measure FC changes as low as 1 ppm when FC is high.

The chlorine consumption is very low: I added about 13ppm five days ago, and now about 8-10ppm FC is left. I thought that such a low consumption was a good indication that the water is free from algae?

If it is very likely that high CYA is my problem, then maybe my easiest option is to drain completely, clean and refill. What do you think?

 

[frogabog]

Do an OLCT with the diluted sample, it's not the best way to do it but it's better than not doing it.

How does the water look?

There's a chance your shock treatment did the trick of course. It's worked for many pool owners a few times... it also normally doesn't work 100% which is why the information here discourages it.

Is there no other way to check your CYA other than strips? If so, I'd say get some calculations going in the pool calculator and account for every bit of dichlor or trichlor that you've added since filling. Adjust for backwashing and give yourself an estimate of CYA to work with for now. If you feel your CYA is over 100, a drain may be your answer for this season as a partial drain still won't allow you to estimate CYA without a good test.

You haven't posted calcium hardness levels. With the cal-hypo you're using, it could be very high. Probably a good idea to check that out as well. It might give you another good reason to drain.

 

[duraleigh]

Do an OLCT with the diluted sample, it's not the best way to do it but it's better than not doing it.

OP cannot perform an OCLT very well without an FAS/DPD test....the DPD is not accurate enough and does not function at high FC levels.

The three criterias for shocking is surely very good, but impossible for me to follow all the way. I simply have no means of measuring CC when the FC is high (I use DPD 1 and DPD 3 tablets), and I can't measure FC changes as low as 1 ppm when FC is high.

 

[SingingSailor]

How does the water look?

The water is clear, but with deposits forming on the bottom. After scrubbing, the water gets somewhat cloudy and green. Filters darkgreen. Pool sides are NOT slippery.
Typical algae?

Is there no other way to check your CYA other than strips? If so, I'd say get some calculations going in the pool calculator and account for every bit of dichlor or trichlor that you've added since filling. Adjust for backwashing and give yourself an estimate of CYA to work with for now. If you feel your CYA is over 100, a drain may be your answer for this season as a partial drain still won't allow you to estimate CYA without a good test.

No other way to measure at present.
Calculation of added CYA, see first post. Best guess is about 3kg tri+di, giving about 90ppm I think. No backwashing => dilution is very low.

You haven't posted calcium hardness levels. With the cal-hypo you're using, it could be very high. Probably a good idea to check that out as well. It might give you another good reason to drain.

Not an issue for me, since we have very soft tap water. I actually add 2kg of CaCl2 beginning of each season, after filling with fresh water.

The chlorine consumption is very low: I added about 13ppm five days ago, and now about 8-10ppm FC is left. I thought that such a low consumption was a good indication that the water is free from algae?

I would appreciate if someone can confirm that I can have an ongoing algae problem even if FC consumption is very low?


I throw in a last question :
Is it common to have high values of combined chlorine even when the FC is relatively high, e.g. >5-10ppm FC?
I've never bothered about CC unless FC has gone down to below 1ppm, didn't think it would be an issue (and can not measure it anyway )

Thx for a great forum!

 

[SingingSailor]

Finally got a TF-100 test kits - algae or what...?

Hi again,

Now I finally got hold of a TF-100 test kit with the good help of a friend.

Here´s my values:
CYA: 40
FC: 21
CC: 0
Alk: 70
CH: 200
pH: about 7,3 (not measured recently due to high FC)
Temp: 17C (63F)

Recent history:
21/8: Algae had started growing again. Shocked to FC>20 and cleaned
23/8: Used antichlor to reduce chlorine level from about 15 to about 8
30/8: Measured FC to about 8. Algae had started to grow again! Cleaned and shocked to FC about 20-30. Temp about 30C.
1/9: Measured FC to 20-30, no algae. Off for 1 week vacation.
9/9: Measured FC to about 20. Temp. dropped to about 18C when not heating. It seems like there has been some little algae growth during the week!!!???
11/9: Measured with TF-100 with results as above.
Notes: All FC measures before today made with DPD tablets/color chart on diluted pool water. Only chlorine added is the two shock treatments noted above.

Odd findings:
- CYA is lower than expected
- It seems that algae grows at least up to about FC=8, maybe even at FC over 20??
- It seems that chlorine consumption is very low, even with algae in the water.

Can I have "mustard algae" or is it something else? It is growing on the entire pool, mostly on the bottom and on objects in the pool. There's an even layer on the entire bottom, with some "islands" with more growth. No difference on sunny / shade side. Color is green / yellowish in the pool, darkgreen in the filter.

 

[frogabog]

For CYA of 40, your shock level is 13ppm. Algae grows under shock level, so yes once it's bloomed 8ppm won't kill it. 8ppm will however allow you to not fall below the minimum of 3ppm the next day. For maintenance, use 3ppm minimum and 7ppm for your daily high target.

What size sample are you testing with? 10ml or 25ml? (TF100) I ask because if you're using the 25ml sample each drop is equal to .2ppm. The 10ml sample is what you should be using, each drop equals .5ppm. If you used the 25ml sample and counted each drop as .5ppm it could explain the high chlorine reading.

Are you brushing the walls and floor to stir up the algae film? Don't use anything to reduce chlorine, shocking takes time (days) so let it fall to 13ppm and then maintain it till you pass the three criteria.

1) clear water
2) overnight chlorine loss test = 1ppm or less
3) CC =.5ppm or less.

 

[SingingSailor]

Yes, I use the 10ml sample size.
Yes, I have brushed the pool several times.

The three criteria:
1) The water is clear (clears up in a day after brushing the pool)
2) Overnight FC loss: performed three tests yesterday evening and three tests this morning and compared the averages in order to minimize variation (I´m also a newbie with this test kit ) The FC loss is 0.3ppm. (Evening results 18, 19 and 19.5ppm, morning results 18, 19.5 and 18ppm). I have not added chlorine in 14 days now, and I estimate the total chlorine loss these last 14 days to between 5 and 15 ppm.
3) CC is 0.

BUT, it is still growing!!

I attached a picture of the pool bottom. There is thin layer of "algae" all over the pool bottom and walls, with areas of more dense deposits. It can very easily be removed by brushing, resulting in a brown dust spreading in the water. The pattern of the deposits does not match the normal pattern of particles sinking to the bottom, this is something else.

 

[Bama Rambler]

I don't know what it is but if you passed the OCLT then it's almost certainly not algae. Do you live close to an industrial site or near a farm?

 

[SingingSailor]

Thx for you reply.
No, I don't live close to a farm or industry.

Summary as I see it now:
- High FC levels seem to slow down the deposits, but doesn´t stop it completely (constant FC level above 20ppm for over a week)
- I had FC down to 0 and CC of 2 ppm in the beginning of this problem 6 weeks ago, and it seemed related
- Chlorine consumption is low (at least at high FC levels), I now pass OCLT test and the shock criteria
- Deposits are both on bottom and floor, pattern doesn´t look like ordinary solid particles sinking to the bottom.
- Deposits are very easily removed, not like stains
- Color in the pool is yellow/brownish or with a green tint. The filters gets dark green.
- Pool sides are not slippery

What could it be?