I think it is algae now....

[denanbob]

Here were my numbers last night before adding bleach:

TC: 2 (don't have measure for CC)
PH: 7.8
ALK: 120
TH: didn't test, vinyl pool
CYA: 50

15x30 above ground 11,000 gallons.

I added 3 (what I THOUGHT were gallons) of bleach last night, but later found out they are only 3 QTS each. Will test tonight before I add 3 more to see how much has been lost (and how quickly it is burning off). Will try to keep chlorine around 25 for about 5 days or so. Is that a good plan?

[Watermom]

I think 25 is too high for a vinyl pool with cya of 50. Check the chart at the following link. Aim for chlorine of 15 until it is cleared. Try to not let the chlorine level yo-yo up and down. The key to killing algae is to sustain the high cl reading.

http://www.poolforum.com/pf2/showthread.php?t=365

[smallpooldad]

It might be better to bring your pH down to 7.4 as chlorine tends to work better at a lower ph, some say 7.2 but I am not sure if that is ok for a vinyl pool, so I indicated a pH of 7.4. To go from 7.8 to 7.4 you would need to add an additional 17.5 oz of Muriatic acid and also add 15 oz of baking soda to hold your alkalinity at 120, over and above the figures listed below, per every 10,000 gallons.

If you are adding liquid chlorine via 5.25% bleach to get to 15 ppm, you might wish to add approximately 7.53% Muriatic Acid, by volume of the amount of liquid chlorine. This is done to hold the pH at the starting point, assuming you are using 5.25% liquid un-scented bleach; otherwise the pH will rise and the chlorine will be less effective.

If using 6% liquid bleach you will need to add 8.73%, 8% Ultra Bleach (liquid) would need 11.78%.

So if you add 100 oz of 5.25% liquid chlorine you would add 7.5 oz acid, do this every time you add chlorine. Once the chlorine goes over 10 ppm it is harder or impossible to get an accurate pH reading. This would negate this problem. Non-liquid bleach numbers are different.

If you know how to use an Excel spreadsheet, and are technically inclined, the PoolSolutions spreadsheet is excellent for calculating your needs. It can be found here:

http://richardfalk.home.comcast.net/...lEquations.zip

As far as the future goes, once this algae is removed and based on a CyA of 50, you may wish to lower your pH to 7.5 (same as the eye) and and keep your FC at 6 (would kill most algae), you may get away with as low as FC 1.5. Holding a FC of 8 would nearly guarantee no return of mustard algae, see which works for you. At pH of 7.8 you need a little more chlorine (no biggy), minimum FC 2, FC 9 on the max side should assure no return of mustard algae. To kill most algae you would need FC 7.

Please note the above numbers are technically calculated numbers, and could vary from pool to pool eg. one pool may need, FC 7 to kill most algae, another only 5, and another 8. It all depends on your situation, wind, dust load, bugs, debris, leaves, etc.

The FC level needed may even vary at different times of the year depending on your location, the amount of shade your pool receives, and on your mean UV index, see here:

http://www.cpc.ncep.noaa.gov/product..._meanmax.shtml

It seems based on your problem that FC 2, is not a place to be so I would not go that far down at a pH of 7.8, or to 1.5 at 7.5 pH. At least not in July or August as the UV indexes are at their height as are temperatures, normally.

You maybe lucky that using the minimum number controls your problem, if it were me I would start at a FC 6 or 7, depending on where you want your pH to be, and lower the FC to the point where algae is not an issue, possibly no lower than FC 3, which is what the "Best Guess CyA Table" shows. If you raised your CyA you might need to raise the chlorine level, if you lowered the CyA to say 35 you might be able to lower them a little. Please note CyA can only be lowered by draining off water, something you may not wish to do. You will just have to try by trial and error which works best for you. Again it is best to refer to the "Best Guess CyA Table", here:

http://www.poolforum.com/pf2/showthread.php?t=365

An easy way to calculate how much chemical to use is here:


http://www.poolcalculator.com/


Hope this helps.

Aloha

[aylad]

You might want to consider lowering your pH to 7.2, as smallpooldad suggests, prior to shocking the pool, but there is no need to continually add acid as you add chlorine--you may get a very small and very temporary pH rise from adding bleach, but it's nothing permanent. The important thing is to get the chlorine up and keep it up, not letting it yo-yo up and down any more than possible.

I also would leave your TA alone....if it lowers (and it won't by much), then you'll be that much better off. TA of 120 is fine, but lower is even better. Concentrate on the chlorine and algae for now.

Janet

[denanbob]

Thanks everyone! I hope I didn't mess up and add way too much bleach. I added only 2 more jugs yesterday (6 qts.) but when I tested, the water was so dark orange that I couldn't get a good reading. (I only have the WalMart test kit). I diluted 5 times and it was still a light orange color (not yellow at all) and that would be at a 25 TC. I didn't even test any higher mainly because I didn't want to know. haha. I will wait for the bleach to come down to 15-20ish and try to hold it there. The 3 jugs I put in Monday should have only raised it to 15 based on the bleach calc program, but apparently somehow it shot way higher than that (unless the test kit just doesn't work at a certain level of chlorine???). I did not lower the PH before adding the bleach (read this too late), but I have some muriatic acid so I will put some in tonight.

Thanks again for all of the help everyone!

[aylad]

I wouldn't worry about the muriatic acid at this point--the high chlorine levels will give you falsely high pH readings, so you'll have no way to know when you've lowered it too much. Having it higher won't hurt anything, but getting it too low will ruin your liner. Leave the pH alone, and keep the chlorine around 20. You'll have to go a good bit above that to do any damage to your pool, so even if it is way high right now, any damage that was done would already be showing itself.

Janet

[smallpooldad]

Aylad, is correct the pH adjustment for each 100 oz of 5.25% Chlorine in a 10,000 gal pool is only about 0.15 pH to the up side , assuming a rise from FC 2 to FC 15, using 5.25% liquid chlorine, the pH would rise from 7.8 to about 8.3 pH.

As chlorine does work better at a lower pH it might be better to lower it some. For the sake of safety as it seems you are a little unsure of the accuracy of your test kit and starting this late you may want to use half the amounts recommended in my previous post. This should give a generous safety margin.

For the sake of interest chlorine concentration at a pH of 7.5 is approximately 50%, at a pH of 8.3 it is in the area of 15%, so you would need a lot more chlorine to do the job. See here:

http://edis.ifas.ufl.edu/EDISImagePa...RE%201&credits=

In fact generally speaking it is always a good rule when maintaining the pool, to use half the amount of muriatic acid mentioned and then re-check 4 hours later. In this case unfortunately one cannot check as the pH cannot be measured.

I do not know how accurate the Wal-Mart kit is, but the Taylor kit is considered by many to be accurate, so you might want to consider buying it.