Richard,
I recently attended a pool seminar where the recommended FC level was 1-2 PPM in a pool with 50 - 70 PPM of CYA with 70 being the ideal. I asked the lecturer where is the chlorine to sanitise the pool? He said the 1 - 2 PPM of FC, when I stated that this chlorine was going to be bound to the CYA and that 1 - 2 PPM of FC was not suffiecient for a CYA level of 70 PPM and surely he needed more FC to ensure adequate sanitisation he stated that any higher FC would be detrimental to the swimmers. I also mentioned that I run all my pools at between 7% - 10% of the CYA level. He stated that this was far too high and the swimmers would get pool itch and some burning, when I mentioned that I run quite a number of large communal pools at these levels and have done so for some time without a single complaint and infact I get a lot of comments of how nice the water is to swim in, I got the impression that he did not believe me.

He then quizzed me about my qualifications. I replied that I have all the qualifications that I need, real world experience, happy customers and fantastic looking pools.

I do not think that chlorine / CYA relationship is taught here in Europe either.

Please show your instructor the 1974 O'Brien scientific paper and have him read the first part of the INTRODUCTION and the SUMMARY at the end of the paper. Then have him look at the CPO post I wrote including the file of my comments that has charts that may be useful to him and note all of the links to scientific references in my post that he should also look at.

He is simply misinformed because manufacturers have intentionally withheld materially important information that consumers and pool operators need to know to make informed purchase and operational decisions. It's not his fault, but if he continues to teach inaccurate information after you have given him the truth, then he will be responsible for it from this point forward.

I will certainly show him the paper and your rather excellent CPO post which I found to be most informative. After he has read them I will let you know his thoughts on them. Thanks once again for all your great work.

Interesting reading, thanks.

Some thoughts, particularly for constant algae battlers.
Algae requires light and nutrients (P04 and or N03), blocking all light is not possible but can help while treating, while ever organics are added you will always have nutrients, and algae will grow even with nutrient levels lower than testable with common kits. Hence FC is requires or some other inhibitor. However we can reduce these requirements by reducing nutrients, the challenge is to do it cost effectively.
Some ideas, has any one looked into the use of zeolites?, do people test there top up water for nutrients, what about anaerobic filtration for Nitrates, regeneratable ion exchange resins for Phosphates.
I'm thinking more for those that suffer regular algae blooms, bacterial (heterotrophic) blooms can also be reduced by reducing organics, autotrophice bacteria is a different in that it can use no organic energy, so some level of FC, ozone, etc is going to be required.

As the tens of thousands of pool homeowners on this forum and on The PoolForum can attest, you can prevent algae growth using chlorine alone if it is maintained at an appropriate level relative to the CYA level. This works for almost all pools with a failure rate of perhaps 1 in 5000. Once you understand the FC/CYA relationship, you no longer are a constant algae battler.

As for nutrients, the only one that is somewhat easily lowered is the phosphate level, but only for inorganic phosphate (known as orthophosphate). There is no easy way to lower nitrates or organic phosphates. Anaerobic filtration might be practical for an aquarium, but not for the large volumes of a pool. The same is true for ion exchange resins -- OK for smaller quantities of water, but not for pool volumes. One can use Reverse Osmosis (RO) to remove virtually everything in a pool and this is one way to reduce CH as well as CYA, for example, but it's not something to be done frequently as it isn't cheap.

Zeolite does not remove algae nutrients. A fine filtration filter, such as DE, can help remove organic precursors, but that doesn't necessarily lower algae nutrients depending on what is getting into the pool.

Bacteria are even less of a problem than algae in properly maintained pools since they are much easier to kill. So maintaining proper FC/CYA ratios prevents algae growth and also kills bacteria quickly. I have had over 3000 ppb phosphates in my pool as have others and yet algae growth is prevented through maintaining a proper FC relative to the CYA level.

You seem to be looking for a solution to a problem that does not exist when one properly maintains their pool understanding the FC/CYA relationship. Now high bather-load pools such as many commercial and public pools could use supplemental oxidation in order to oxidize organic precursors before chlorine gets to them since that would reduce disinfection by-products and also lower chlorine usage. However, in outdoor residential pools, the bather loads are so low and the sunlight and air circulation are good enough that disinfection by-products are much, much lower. Also, most chlorine loss in residential pools is due to sunlight whereas in commercial/public pools it is due to bather load.

Agree, I was assuming from my short time and reading here that some people might be having problems, this may not be the case or a case of poor FC/CYA management.

Simply for the purpose of the discussion, not to suggest its a better method.
If a pool was high in Organic Phosphates, it could be fixed over the closed season. Grow algae and harvest, this would reduce nitrates also.
A set up similar to a sand filter with flow or media that has anaerobic states would maintain nitrates,
Of cause filling the pool via RO is ideal if water wastage and costs are not an issue, prevention is better than a cure.

Zeolites can take up Ammonia, therefor there is less nitrite>nitrate. It would also have low oxygen states with in the rock so would provide anaerobic conditions to aid in reduction of Nitrate to Nitrogen via bacteria.

There are many other methods to reduce algae, these are just ideas that I have not seen mentioned so I put them out for food for thought for the more experienced pool enthusiest, I'm happy to start my pool husbandry learning curve of with traditional pooven methods.

This is simply not true in a pool with chlorine in it. Chlorine combines with ammonia VERY quickly to form monochloramine, in a matter of seconds if there is no CYA to a matter of a minute or two when CYA is present, such that ammonia will never reach the zeolite filter. The zeolite will not absorb nor breakdown monochloramine and the release of ammonia from monochloramine is so slow that the monochloramine will get fully oxidized by chlorine (mostly complete in a matter of hours) long before enough ammonia is released from monochloramine to get absorbed into the zeolite filter. This whole marketing campaign for zeolites saying "no ammonia, no chloramines" is just bunk -- not that it isn't true, because without ammonia one can not have chloramines, but that it is terribly misleading because the ammonia doesn't survive long enough to make it to the zeolite filter.

As for bacteria converting nitrate to nitrogen, again this won't happen in a chlorinated pool because the chlorine will kill bacteria -- that's the whole point of chlorinating the pool.