high cya, how to reduce it?

Hi, I've read tons of helpful material here on poolforum and also on the poolsolutions website. My problem is that I have high chlorine but algae is growing in my pool. After doing some research I've determined my stabilizer is too high and I would need over 8ppm chlorine to kill algae (based on the Best Guess Chlorine Calculator)

Here are my test results:
Free Chlorine: 4ppm
Total Chlorine: 4ppm
ph: 7.5
Hardness: 270ppm
Alkalinity: 90ppm
CYA: 100ppm

My question is can I reduce the CYA? Or is my only option to stop using pucks and wait? (how long would that take?) In the meantime, should I kill algae by increasing chlorine levels to over 8ppm? Or just let the algae get out of control until the CYA comes down and my chlorine starts working?

Help!

Gary

Hi gvon and welcome to the Pool Forum. You have some misinformation. With a cya reading of 100, it is going to take a shock level of 25ppm of chlorine to kill the algae. Take a look at the Best Guess chart again. 8-15 is the maintenance level for chlorine but is way too low to kill algae. In addition, test kits cannot differentiate over 100 so in fact, your cya could actually be even higher than that!

The only way to reduce cya is to do a partial drain and refill. You can probably safely drain 2/3 of your water and refill but do NOT totally drain your pool. If you don't want to drain, you can manage a high cya pool with the higher cl levels i wrote above. Your choice. Either way you must stop using the pucks and also do not use any dichlor shock powder as it also will cause your cya to continue to climb. Just use bleach for your source of chlorine.

What kind of pool is this and what volume? What type of filter and size of pump? Do you have a good test kit? If not, you will need one that is capable of reading high chlorine levels. We suggest the Taylor K-2006 or 2006C which is the same kit with larger quantities of some of the most used reagents. Click on the Amazon link in my signature below and you can order it and the Pool Forum makes a little money in the process which helps keep us online. Only order if the seller is Amato Industries, however. Some other sellers are substituting the K-2005 which you do not want.

Repost with requested info and somebody can help you get this cleared up.

Thank you for the quick reply! It's a 10k gallon fiberglass pool with a 1.5hp hayward superpump and sand filter. I currently use test strips that measures FC, pH and Alkalinity, and I get my water tested at the pool store every other week. The results I posted above were from the pool store. I would rather drain and refill to run lower chlorine levels, however I would be refilling with well water with high levels of iron, so I'm undecided on the best approach right now.

Well water presents a whole other set of problems. Before you decide, go and read some of the posts in the Stains and Metal Matters section of the forum. A lot of people using well water have a lot of problems. Think about it and then come ask questions if you need to before deciding. Any possibility of trucking in water?

EDIT -- I'm not sure, but I think you may have to log out to be able to see that Metals section of the forum. Try it first while logged in but if that doesn't work, log out and try again.

Hi Gvon;

3 options:

#1 - drain 2/3 of your pool and refill. Risky with an AG pool or a concrete pool if the water table is high; impossible on a vinyl pool without special preparations. PLUS, then you have to refill with iron contaminated water and deal with all that.

#2 - use a sodium bromide (Yellow Treat, other products) to 'de-stabilize' a small portion of your chlorine and turn it into bromine. The downside is that, not only will this consume some chlorine now, but it will result in much higher chlorine consumption over the next few weeks, even after the algae is gone.

#3 - use the Best Guess Chart to run a high chlorine pool. You'll need to get a DPD-FAS testkit, to do this, since only these kits can test the high levels of chlorine you'll have accurately. The upside of this is that you'll be able to chlorinate just 1 or 2x weekly. BTW, there is no really danger to high chlorine + high stabilizer in an outdoor pool.

Since you already have algae my suggestion would be the following:

1. Order a DPD-FAS kit (Amazon link below)
2. Purchase an cheap OTO/phenol red kit at Kmart, Lowes, etc. and use it, for now. Goofy strips produce unreliable readings, even when read by the dealer gizmo.
3. Dose with 2 gallons of plain 6% household bleach as soon as possible. (Doesn't have to be in the evening, since your CYA is so high.)
4. Go by a pool dealer, if you can, and purchase a sodium bromide based granular algae product. Use ONLY 1/4 of the recommended dose!
5. Use the OTO test kit and bleach to maintain a DARK yellow chlorine level (~10 ppm)
6. Once you get the DPD-FAS kit, if you still have algae, gradually increment your chlorine level up, till you reach 25 ppm OR the algae is gone.

Ben