I'm working on a LARGE pool, 1/2 olympic I believe. There is an algae problem (some blotches on the bottom of the pool) which has created a "boatswimmer" problem (only in the corners). One of the guys hit the panic button and wants to drain the pool.. Is this the most sound way to treat the problem? According to what I've read on this incredibley informative site, draining may not be the wisest way to go. It's a chlorine pool:
PH 7.5
FC ON AVERAGE 3.5 but it has dipped below that number often.

We have a liquid CL injection pump. However, I believe that from constant adjustment by my peers trying to find a "sweet spot" that holds the FC level at 3.0-3.5 ppm constantly, the pool has been unbalanced for some time. Also, I've read here that 3.0-7.0 FC is the range which leads me to believe that 4-6 ppm FC is a better range to hold. So to drain or not to drain....?? A confused plumber tasked with a pool... sigh.

Welcome to TFP!

We rarely advocate a full drain and refill on a pool. Doing so with a pool of that size would probably not be necessary. Can you post a full set of test results for us to look at? We need to see FC, CC, CYA, CH, and TA. You've already posted the pH (which looks fine). Just let us have the rest and we can go from there.

Thanks, glad to be here
Unfortunately, at the end of my shift. I was informed that the pool is to be drained. When I go on shift this evening, the day crew should be well into the process. This is unfortunate, I showed them all of the information on this site...

Thank you for trying to do the right thing. Draining a pool of that size without knowledge of water chemistry is near criminal. What a huge waste of a precious resource. Whom ever made that call has no respect for water and doesn't deserve to be in that position. When the water bill comes due if there is somebody in authority above that person I would explain the situation. Let them know one knowledgeable person needs to be in control of the water chemisty and make that person YOU.

It is fairly common practice to drain and refill commericial pools and may be required in certain areas. This is a case where training and education can help. Sometimes it doesn't happen overnight. Additionally, it may not have been the pool caretaker's call to make. It appears that the OP would like to effect the changes that we promote but he obviously has other employees involved. Therefore, we can offer our advice and reasoning to him and politely support him in hope that he is able to make the transition to a BBB type water management philosophy in the future.

No big deal. Just stick around and keep learning. There is a lot of good information on this site for you to use.

Sorry if I seemed overdramatic. I know nothing of maintaining a public pool. Just seems a waste to loose all that water. Water is just one of the many things we take for granted in our bountiful country. I hope the resources remain for my grandchildren one day.

To the OP, keep reading and posting here. Maybe you can slowly make changes were you work.

Not all hope is lost, there are several repairs that can be made with the pool drained i.e. lights changed x 5, tile repair and replacement x ??? Should be filling in 2 days... I will keep you posted and once the pool is up and running I will be running the chem show vicariously through this site

Congrats on the promotion. Are you CPO certified? Lots if help here for you. You can have the best pool in town. Have you read chem geeks "what is not taught in CPO training" thread? It's in the deep end. Post with questions as they come.

Ok Pool Peoples... I was on vacation, the pool was empty the day I left. I came back and noticed last night that they were keeping the CL below 3.0 ppm.... after having drained the pool to get rid of algae, I (being the night guy) so first thing this morning when ppl showed up I was very adamant in telling them that "4.5ppm is the ideal, its safe, it gives us a bit of leeway with regard to algae growth"... I was told that this would not happen and that 3.0-3.5 is where the "kids" (I'm older than those I work with) were going to keep it.... 3.0ppm is where they tried to keep it prior to draining the pool... they couldn't, I did research and found this site (this is a very good thing). Regardless of contributors vast experience over mine and the "kids" it seems, the pool is destined to grow algae. If one of you could point me to a pdf document or copy and paste something that in black and white gives good ppm levels into here I would gladly print it and show it. Thanks so much for your responses to this situation, and hopefully I can find someway to get them to listen....

If the stabilizer/cyanuric acid/CYA level is low enough, say around 20 ppm, a 3ppm level of free chlorine (FC) is OK.

The appropriate FC level is dependent on the CYA level. There's a good discussion in the Pool School on this concept.

Also, you should familiarize yourself with any local pool requirements. I found the Fairfax County, VA ordinances for commercial pools on line. Here, for instance, the max CYA is 50. Max & min FC levels are given, too.

Good luck!