Don't swim in that old, nasty pool water... seriously!
The pool service industry is complex and every-changing. Pools are becoming artwork, but what's the most important part to keeping this art looking good? A cleaning service? I wont say no, because we wouldn't be in business then! I tell my customers, we are important but not magicians either. Our techs do a pretty spectacular job, but ultimately we are at the mercy of the pool.
The old verbiage that we here all the time. "I have never drained my pool." And to that my response is... "Do you drain your bath water?" Now obviously the only similarity is that they both are bowls filled with water. And most people don't even take baths anyways. But we are all familiar with baths, bath water, and how nasty bath water becomes.
Once we become somewhat relatable, we can move on to the science behind old, nasty pool water. First, we must break down the process of how a pool works, and how it stays nice and clean day after day, month after month. Filtration, and chemicals. That is it. I will get more in depth with that in a different article, since that is not relevant to your old, nasty pool water!
Oh by the way, you can have crystal clear water, and it still be past its expiration. In fact I once had a lady who had not drained her pool in 25 years. We could even register some of the readings. Those values would have probably made it to the moon. Her pool was consuming chemicals, like an infant bottle feeding every 3 hours. She though this was normal.
Lets take a step back. Pools SHOULD NOT need an abundance in chemicals to stay sanitary and clean. End of story. Pool companies should be looking out for your best interest. Most companies upcharge for chemicals, and therefore will let pool water go beyond their shelf life, as your bill increases year after year (besides inflation). The pool professionals goal is to use the bare minimum to keep your pool water healthy.
With that being established, how often should that old, nasty water be changed? From what we have seen servicing thousands of pools over the years; 3 years. After that the clock usually strikes midnight. Chemical consumption in the fourth summer booms. We are writing this based on the climate we experience in Arizona.
In a perfect world pools would be drained every 2 years. "But isn't this a waste of water, when cities are experiencing such droughts?" The water is drained to be recycled by your city, so negative Batman. Now if you drain into your lawn or a field, then yes. So this is not a valid excuse.
Ok now to the science. Pool primary way of staying sanitized is from chlorine. Yes this includes salt systems. Remember salt is NaCl, aka Sodium Chloride. Chlorine breaks down in two ways. Destroying organic matter (bacteria), and UV light. Well we don't want the chlorine to burn off before being able to do its job, right? So we need to add a stabilizer to the water. This is called conditioner, but scientifically is known as Cyanuric Acid. The ideal levels in a pool exposed to the sun, is roughly 50-80ppm. We personally think 30ppm is a good starting point. Remember these values for later.
The primary chemical used in pools is stabilized tablets, placed in tab floaters. These are 99% Tri-Chlor. Tri-Chlor has 3 particles of chlorine to 1 particle of cyanuric acid. So 1 tab will raise your chlorine 3ppm and will raise your CYA 1ppm per 10,000 gallons of water. Lets just say an average play pool is 10,000 gallons. Lets say it goes through 3 tabs a week for 20 weeks (peak of summer) Math says this, 20 weeks x 3 tabs x 1 ppm CYA = 60 ppm CYA added to your pool. Even if we average the 1 tab per week the rest of the year, that's an additional 32 ppm of CYA added to your pool. So in one year we added over 100ppm of CYA in most pools.
Is there anyway to avoid this? Yes and no. Salt systems don't produce CYA when they produce chlorine, so the CYA levels don't increase. However in the winter, salt systems usually shut down due to the cold water. Then we switch to tabs and we start the increase of CYA. There are also other forms of "shock" or more soluble chlorine. Liquid chlorine only adds salt as a byproduct and cal-hypo adds... you guessed it, calcium as a byproduct. FYI, calcium is no better than CYA...
The magic number for CYA is 200ppm. After we pass that, the pool turns into a monster, out to feast. So you may be asking yourself. "Shouldn't I drain every 2 years then?" A good pool company will not use tabs in the cooler months. Algae and bacteria don't fare well in sub 50 degree water. Algae's favorite temp is a toasty 88 degrees. You should be using liquid chlorine to sanitize in the cooler months. If we can get CYA to only add about 70ppm per year, we can make it through 3 full years!
Now we can still battle a pool between 200-300ppm of CYA with some knowledge. That's at least something we hold over old pool water. But after 300ppm getting ready for some algae welcoming parties! Yes, even with a pool service! CYA and Chlorine are buddies. As one grows the other must grow. Once CYA hits 300ppm chlorine has to remain at a 10ppm to even sanitize properly.
Lets go back to that lady who didn't drain her pool in 25 years. Her levels had to be 5000ppm if not more. And eventually you hit the point of no return! As the pool requires more and more chlorine, you give the pool more and more chlorine, exponentially increasing your CYA to the pool. Its a nasty relationship, and you need to breakup.
Sadly, this isn't the only thing that comes with old, nasty pool water! Calcium. Its great in moderation, but bad to over indulge. Most tap water in Arizona ranges from 100-150ppm. This is an ideal number, its keeps your pool nice and h... firm. But water evaporates, and calcium is too lazy to tag along. The end result is overcrowding! After about 3 years your calcium level in your pool is around 1000ppm. Levels that high give you a nice ring on the tile, and calcium starts to stick to everything else.
So if your pool has over 200ppm (maybe we will let it slide to 300ppm) of CYA and 1000ppm of hardness in the pool, it's time to breakup with your pool water. Trust us, the next batch will be that as fresh as it gets, promise!