Many Pools Get Algae; In Any Given Year Most Do Not
At least a million pools DO get algae in any given year. There are around 10 million residential pools in the U.S., about half in-ground and half above-ground. Why do you think pool stores stock and sell so much algaecide, phosphate remover, clarifiers, flocculants, enzymes and "shock" products? Do you think they would have these and that manufacturers would make them if they were not regularly sold and used? If only 10% of all pools got algae in a year, then that's 1 million pools. The real number getting algae is probably higher (perhaps up to 20% for pools using Trichlor-only), but at such percentages many pools don't get algae during one or a few seasons and then wham, they have a problem. Some pools never have a problem.
Low FC / High CYA Alone Doesn't Cause Algae; Algae Needs Nutrients
You see, it's a statistical thing since algae growth isn't a certainty just because the CYA level gets high. If a pool is poor in algae nutrients (phosphates and nitrates), then it won't take as much active chlorine to kill it faster than it can grow so you can have the CYA get quite high before algae becomes an issue.
CYA Can Be Kept Low By Dilution That Isn't Intentional
Smaller pools with shorter swim seasons and/or sand filters getting backwashed weekly and/or summer rain overflow can all help keep CYA levels in check. Winter rains, a partial drain when closing a pool, and bacteria conversion of CYA into ammonia, nitrogen gas, nitrite or nitrate can all lower CYA levels each season. And some pool owners intentionally do partial drain/refill when the CYA gets high if their pool store tells them to do so (usually not until it's well above 100 or sometimes 200, however). Nevertheless, it's no coincidence that most pool problems occur in August near the end of the swim season when CYA is typically highest.
Weekly Shocking, Algaecides, Phosphate Removers Can All Reduce Likelihood Of Algae
Many pool owners shock their pools weekly which helps make up for too low active chlorine levels during the week. Some use algaecides or phosphate removers. Remember, we never said that they didn't work, but rather that they were not necessary if one maintained the proper Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level.
Some People Driven To SWGs When Fed Up With Trichlor
And then there's the mass movement of both existing and new pools to use saltwater chlorine generators (SWGs). Do you think that was just to avoid having to buy Trichlor pucks/tabs? Trichlor is pretty convenient. A big push towards SWGs comes from people getting sick and tired of their pool either getting algae or looking dull/cloudy. SWGs aren't just about convenience, but about being relatively more algae-free compared to Trichlor-only pools. Now even SWGs run under recommended levels from manufacturers can get algae (i.e. 1-3 ppm FC with 60-80 ppm CYA), but the CYA level doesn't climb so most don't and if one follows the slightly higher 4 ppm FC with 80 ppm CYA then SWG pools are generally in good shape.
Algae Problems Reported Frequently Every Year
Also, sites like this one, The PoolForum, and other pool sites wouldn't get the traffic they do with many reports every season of algae-filled or cloudy or problem pools from new members if it wasn't a real problem. It's not just nearly 40,000 members here at TFP, but over
1/4 million unique visitors during each peak month (May, June, July) this year (i.e. people who read but don't sign up or post) and the site is still growing rapidly.
My Own Experience
In my own pool 9 years ago, I used Trichlor pucks/tabs and had no problem during my first year. However, I was using algaecide though only every other week. I started having problems in the middle of my second season where I had a mysterious increase in chlorine demand and had to use more pucks/tabs to keep up. Then the water started looking dull and then cloudy. It was an impending algae bloom, though I didn't know it at the time. My CYA had risen from 30 ppm to 150 ppm over 11 active (non-winter) months. I have a mostly opaque electric safety cover so my chlorine usage was a fairly low 0.7 ppm FC per day since the pool was used 2-3 times per week (we use it every day now) and originally could maintain my 3 ppm FC target adding an additional 3" 8-ounce Trichlor puck every 5 days in a floating feeder. 11*30*0.7*0.61 + 30 = 171 ppm and with some splash out and slow oxidation of CYA from chlorine the result of 150 ppm is perfectly consistent with prediction. I have an oversized cartridge filter that only needs cleaning once a year so contributes almost nothing to water dilution. We get almost no summer rains and during the winter I used a pool cover pump and put the water into the sewer, not into the pool. So I had virtually no water dilution. I also have 400 ppb phosphates in my fill water and used metal sequestrants that were phosphate-based as well as non-chlorine shock, clarifier and enzymes (everything that was recommended by the pool industry). That's when I found The PoolForum, switched to using 12.5% chlorinating liquid, and never looked back.
Testing Is Quick And Not A Chore
Because of my mostly opaque electric safety cover, I only test and add chlorine twice a week, but my chlorine usage is so stable that even if I had to add chlorine every day or two without a cover, I'd probably not have to test every day. There's no way you should be spending an hour doing testing. Only FC and pH need to be tested most frequently. TA and CH and CYA don't change frequently enough to test that often. I only test these three times, once at the start, once in the middle, and once at the end of the season. Some pools might need a little more frequent testing of these if they change a lot, such as CH rising quickly from evaporation and refill with water high in CH, but still not that frequently (certainly not daily and probably not weekly either). The most time consuming part of my pool maintenance is something I need to do regardless of chlorine source and that is brushing the pool (usually weekly during the summer) and cleaning out the skimmer basket, the pool sweep bag, and when needed the pump basket.
People Don't Always Tell You The Whole Story
By the way, to the guys that told you "they rarely have to add acid", ask them how often they are adding pH Up and/or Alkalinity Up? They are still adding something in addition to Trichlor. For every pound (16 ounces weight) of Trichlor, you'd have to add 12 to 27 ounces weight of pH Up to maintain TA and pH (one or the other -- you can't do both equally using pH Up alone). Also, people may not be telling you that they shock weekly or use algaecides or phosphate removers or have copper in their Trichlor pucks. There's no question Trichlor can be more convenient because it takes about 5 days for a tablet/puck to dissolve in a floating feeder, but that's its only real advantage.