Cannot get rid of the algae !!

[jenner]

I have a gunite inground pool - 25,000 gallons. 4 years old.Current readings are:

PH: 7.4
TA: 130
CYA: 100+

I have had clear water all year - no problems. A couple of weeks ago I turned on the solar heating to extend the swimming period - I live in California so pool is open all year round. Pool was being kept at around 83 degrees. Noticed algae last week so dumped in 5x3quarts of bleach, brushed pool and cleaned cartridge filter. Put in another 3x3quarts 3 days later as pool was still somewhat cloudy. Then another 2x3 quarts yesterday. Been running the filter from 9am to 12 midnight. (equipment is near property boundary so concerned about noise to neighbour) Chlorine level is approx 25ppm (tested on Guardex kit using pool water and distilled water method) but pool is not clearing. What am I doing wrong? - this method worked last year which was the last time I had algae. Solar heating turned off and pool now running at 76 degrees. I know that my high CYA reduces the chlorine affectiveness so have kept chlorine levels about 10-12 throught year. I "shock" with bleach and also have trichlo pucks in online feeder. Should I put in more bleach? - will that damage my pool? Many thanks

[chem geek]

Your high CYA requires higher levels of chlorine to be used. Though Ben's chart tracks the disinfecting chlorine level quite well for the Min/Max columns, the Shock column seems to drop off too quickly at high CYA levels. This chart shows the amount of FC needed at various levels of CYA to achieve the desired (column heading) disinfecting chlorine level. The columns to "shock" regular green algae appears to be around 0.2 or 0.3 ppm disinfecting chlorine so that would imply 30-40 ppm FC if the CYA were 100 ppm. If your CYA were actually higher than that, then you may need even more. It's roughly proportional -- to get to the 0.2 to 0.3 ppm of disinfecting chlorine you need your FC to be about 30%-40% of your CYA level.

At least you don't seem to have yellow/mustard algae. That nasty stuff appears to need 1.0 ppm disinfecting chlorine which would require 65 ppm FC -- yikes!

I suggest you boost up the chlorine to the 30-40 ppm FC level and see if it starts to clear. I also suggest you stop using trichlor pucks (in your feeder or anywhere) since they add to the CYA level. Just use liquid chlorine (or bleach) and only use trichlor pucks when your CYA is low, say below 30. A CYA of 100+ is a problem, but fortunately your CYA may drop over the winter (otherwise, you'll have to drain and refill to reduce it). You might consider using the winter rains to dilute your pool since that will reduce the CYA (but will reduce everything else as well so you'll have to add back some calcium and bicarbonate).

The fact that you got algae in the first place while having the chlorine level at 10-12 (did I understand that correctly?) may mean that your CYA is considerably higher than 100 ppm. If it were 150 ppm or 200 ppm then even your 10 ppm FC would probably not be enough to prevent algae.

Richard

[fcfrey]

Assuming that your CYA is between 100 and 200 you need to shock to 25 ppm and keep it there continuously for a few days. That means 10.4 gallons for your 25000 gallon pool (if you are starting at 0 and if you have algae you probably are). That is the starting dose ---- Test several times per day to monitor where the level is and add bleach per the bleach calculator to keep it at 25 ppm continuously (NO YO-YO). Once it stabilizes with the algae gone you can let the FC drop back to 8-15 ppm.

You really need to get your CYA down so that means stop using pucks and partially drain and refill until you get below 50ppm CYA. You can use the sheet method or the silage bags to fill with water without risking pool damage. There are several posts about how to do that on this site.

Post your test results and keep us informed. Good Luck!!

Edit: Looks like Richard beat me to the punch --- His advise is good.

[doggie]

Jenner, have you been needing to add PH increaser often or does it stay at 7.4 on it's own?

[jenner]

No, I have not had to use PH increaser ever. My PH is pretty constant at around 7.4/7.6 with my TA usually around 120. For the past few weeks due to my TA going up to 160 I've been using the Muriatic acid + airating method for bringing the TA down. That seems to have worked as my TA is now lower.

[doggie]

I was curious about the PH because mine was always too low, and I was constantly having to add LOTS of PH increaser. Also, my CYA was well over 100. The pucks were the culprit in both cases.

I've since sold all my pucks dirt cheap. All 60 pounds of them. (yes, I had just gotten more!) But I didn't want to be tempted to ever use them.

Nothing but bleach for us from now on!

[chem geek]

No, I have not had to use PH increaser ever. My PH is pretty constant at around 7.4/7.6 with my TA usually around 120. For the past few weeks due to my TA going up to 160 I've been using the Muriatic acid + airating method for bringing the TA down. That seems to have worked as my TA is now lower.

jenner, it is unusual (actually impossible, as far as I know) for TA to go up unless you add pH increaser that is sodium carbonate or add alkalinity up that is sodium bicarbonate or you refill water that has evaporated with fill water that is high in TA. Adding Borax makes the TA go up a little, but not much. Have you tested your fill water and is it high in TA?

Richard

[CarlD]

You've gotten good advice. Now go find the stickies on Algae.

You need a lot of one more ingredient: P.O.P.P.

Pool Owner Patience and Persistence!

[jenner]

This is in response to Chemgeek's query at to my fill water being high in TA.
Just tested my tap water, which is what I top up/refill my pool with and the TA test shows TA at 100. This is pretty average isn't it?. However, whenever I have topped up my pool during the summer the TA level goes up in the pool and I lower it with Muriatic acid.

Thank you for all your help. The algae is definitely clearing and the pool is much clearer but with the CYA so high I'm always going to be battling unless I use very high dosages of chlorine. So I am now intending to half to three quarters drain the pool. We don't get enough rains here in California to make a real difference (unless you count the ones we got in 2003)

I'll let you know how I get on

[chem geek]

This is in response to Chemgeek's query at to my fill water being high in TA.
Just tested my tap water, which is what I top up/refill my pool with and the TA test shows TA at 100. This is pretty average isn't it?. However, whenever I have topped up my pool during the summer the TA level goes up in the pool and I lower it with Muriatic acid.

Actually, with fill water that has any significant amount of TA, and 100 is significant though not huge, you will increase your TA over time IF your pool water evaporates and you fill with new water that contains any TA in it. So it is quite possible that if you are filling up due to evaporation that your TA will increase (assuming your pH remains constant). The other way that TA will increase is if the pH rises over time, but adding acid will lower both the pH and the TA. I suspect there might be a little bit of both going on. Only if you splash out water or backwash a filter and then refill would I expect the TA to slightly go down rather than up. When you do the drain and refill to reduce CYA, you will find that your TA will go down towards the 100 of the fill water.

Thanks for giving me more details. And congratulations on your pool clearing up -- it's on its way so as Carl says, Patience, Patience, Patience.

Richard