Can algae grow without phosphates?

[TreeFiter]

I'm not sure what got me thinking about the subject, but the other day I was wondering if it was possible for algae to grow in a pool with no phosphates.

I realize phosphates can be a touchy subject, and I'm not by any means recommending that anyone should rely on regular phosphate treatments to prevent algae growth in their pool, but I can see certain situations where it might be the quickest/easiest/cheapest way to clearing up a pool or even preventing an algae bloom.

So can algae grow without phosphates? It seems to me like if there is no food, it would be hard for algae to live.

 

[JasonLion]

Algae requires phosphates, period. No phosphate, no algae. However, there are various forms of phosphate. Not all of the forms that algae can use can be removed and not all of the forms algae can use show up on the common tests. The test and the remover both work with the most common forms of phosphates, but there can be other forms now and then.

Phosphate remover is only a good deal financially if your natural phosphate level is very low to start with (which is rare). In nearly all cases simply maintaining an appropriate FC level is easier and less expensive than phosphate remover.

 

[TreeFiter]

Thanks Jason. Kind of what I suspected. In the pools I deal with, the source water is usually phosphate free. I've noticed a connection between using sequestrants and elevated phosphate levels, and certain pools just seem to accumulate phosphates over time. I did come across a few situations last season where a phosphate treatment worked out to be the best course of action. (I was resistant to doing the phosphate treatment, but once we did it, the pool came around quickly.)

If a pool turns, and you SLAM it, you could easily use up $50 in chlorine (about 8lbs of trichlor shock). If a bottle of phosphate remover is about $50, it doesn't take long before you break even.

Like you say "maintaining an appropriate FC level" is key, but once it goes wrong, I'm starting to think the phosphate remover can be your friend. Certainly depends on the situation, but in the situations I see, where good fill water is readily available, a phosphate treatment could be a quick fix.

We are talking about fairly specific situations here. I'm not suggesting that everyone should rush out and buy phosphate remover and treat their pools as soon as a test says they have phosphates, but to me it makes sense that if you can quickly cut off the food supply to the algae, you can end a green pool situation fairly quick.

 

[bobodaclown]

I'd recommend using liquid chlorine vice trichlor.

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[TreeFiter]

I'd recommend using liquid chlorine vice trichlor.

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Good suggestion. Even with liquid, it is pretty easy to spend the $50 it would cost for the phosphate remover.

A bit of an ironic side note: Early this winter my boss brought me in to straighten out a problem with an indoor pool. My boss insisted on doing a phosphate treatment rather than taking my advice to stay on top of the Bromine levels until the algae was killed. Today (a few months later) he called me again because he needs someone to do another phosphate treatment. He refuses to understand that the problem isn't phosphates. I should mention that when I maintained this pool all summer long, there were no issues, but when it was handed off to someone else for the winter, it has turned twice...Must be the phosphates

 

[JasonLion]

There is a little more to it than that. Algae has phosphate in it. If the algae dies, there is again phosphate in the water, and new algae can grow. Thus, phosphate remover isn't always a very good way to fight pre-existing algae. It will slow the algae growth rate down, but not cure a major algae problem all by it's self. The net result is you end up using some chlorine anyway.

Also, you mentioned this above, but it is worth pointing out again, that you are working on the assumption that the phosphate level is low to begin with. Otherwise it can take way more than one bottle of phosphate remove.

And just to be through, phosphate remover can cause problems of it's own. Now and again it will turn the pool into a cloudy mess that is difficult to clean up. Also, if your phosphate level is quite high, phosphate remover can clog up the filter almost instantly, and in very severe cases damage the filter.

 

[TreeFiter]

There is a little more to it than that. Algae has phosphate in it. If the algae dies, there is again phosphate in the water, and new algae can grow. Thus, phosphate remover isn't always a very good way to fight pre-existing algae. It will slow the algae growth rate down, but not cure a major algae problem all by it's self. The net result is you end up using some chlorine anyway.

Also, you mentioned this above, but it is worth pointing out again, that you are working on the assumption that the phosphate level is low to begin with. Otherwise it can take way more than one bottle of phosphate remove.

And just to be through, phosphate remover can cause problems of it's own. Now and again it will turn the pool into a cloudy mess that is difficult to clean up. Also, if your phosphate level is quite high, phosphate remover can clog up the filter almost instantly, and in very severe cases damage the filter.

All very good points. It certainly depends on the individual situation.

 

[chem geek]

Also, you are servicing pools which is different than a homeowner who is maintaining their own pool on a daily or near-daily basis. For pool services that don't visit a pool that often, then having "insurance" against algae growth can be worthwhile, but there are all sorts of caveats as Jason mentioned.

As for metal sequestrants increasing phosphate levels, that is true for some sequenstrants including those containing HEDP.

So if you have a pool with primarily orthophosphate and not organic phosphates and no algae and there are not phosphates in the fill water (or you have a pool cover for minimal evaporation and refill) or other sources introducing more phosphate, and if the phosphate level isn't so high as to cause problems during removal (excessive cloudiness or filter clogging), then using a phosphate remover can work reasonably well. It would be insurance and is not necessary.

I used to have 3000+ ppb phosphates in my pool, probably from using HEDP metal sequestrants (I used all kinds of products when I first got my pool before learning how to properly maintain it) and from the 400 ppb phosphate in my fill water. The pool was easily maintained with the proper FC/CYA ratio, but if the FC ever got too low there was a noticeable increase in chlorine demand as algae could start to grow and use up chlorine. I would describe the pool as "reactive". Nevertheless, I was able to maintain the pool well until I neglected to add chlorine fast enough after opening one spring and turning on the solar panels (that were probably dirty inside so consumed chlorine faster). As described in the thread It Can Happen to Anyone - Zero Chlorine, CYA-->Ammonia, the chlorine level got low, algae started to grow, chlorine level more rapidly got to zero, bacteria then grew and converted CYA into ammonia and partially broken down CYA chemicals creating a HUGE chlorine demand. I got threw it and the next year as described in the the thread Orenda Technologies PR-10000 and CV-700 Products I got a free phosphate removal treatment (and enzyme treatment) which clouded the pool where I used a clarifier to more quickly clear it (my wife wanted to swim the next morning). Ever since then, my pool is no longer "reactive" and if the chlorine gets too low it doesn't show any noticeable increase in chlorine demand. Though I have 400 ppb phosphates in my fill water, my use of a cover means there is minimal evaporation and refill. Furthermore, the annual winter rains dilute the water to keep everything in check (mostly the salt level).

With all the caveats we don't recommend using a phosphate remover, but that does not mean that it doesn't work to significantly slow down algae growth, at least in certain situations.

 

[TreeFiter]

I'm looking at it as another tool in my toolbox. It has its purpose, even if that purpose is limited. I have really steered away from using phosphate removers, but there have been a few pools where the circumstances limited the use of other options. For example, the pool I mentioned above, an indoor pool using Bromine. This is the second time my boss has decided to do a phosphate treatment this winter. The first time, I attacked the pool with chlorine. The problem was that the Chloramine odor filled the room to the point where I had to get out. So I couldn't just load up this pool with chlorine and walk away, without filling the entire house with harmful gasses. Since it was a Bromine pool, I also tried adding MPS, but I still wasn't getting results. At this point, my boss was looking for something else to blame, rather than put the time into daily visits to keep the Chlorine/Bromine up. So he decided (for all the wrong reasons) we should treat for phosphates. He got lucky, and once the phosphates were removed, the pool cleared right up.

So what I took away from this experience was that sometimes a phosphate treatment might be the shortest path to a clear pool. Again, it is going to depend on the situation, and usually isn't where you want to start, but it can work.

 

[chem geek]

The other time it can be useful is if one has yellow/mustard algae and is unable to completely get rid of it or if it gets frequently re-introduced. One could operate at a higher FC/CYA ratio (around 15%) to keep that algae from growing, but in an outdoor pool that means twice the chlorine loss from sunlight and roughly twice the overall chlorine demand. So use of an algaecide or phosphate remover is an alternative which may be helpful, if the caveats are not applicable to that pool.