Clean Water in the Swimming Pool

Crystal-clear, hygienically clean water that’s the prerequisite for pure enjoyment. Unfortunately, reality often looks quite different, even though water care really isn’t rocket science. As is so often the case, our blog posts about swimming pools are based on current customer questions.

This week we received a call from a relatively new pool owner who told me, horrified, that there was constantly dirt in his pool. He filters, backwashes, vacuums – and yet there’s still dirt in the water.

That’s normal in itself; something always falls into the pool, and shortly after the pool is installed, there are still a lot of dust particles in the water from cutting stones, pouring concrete, etc. It takes a little while for this dirt to be filtered out of the water. But when he admitted, after persistent questioning, that he runs the filter system for a full two hours a day in a 40 cubic meter pool and switches it off completely when the pool isn’t being used, I explained the basics of water care to him again.

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Water treatment basically consists of two pillars: physical and chemical treatment.

Pool water is full of dirt from outside: leaves, mosquitoes, dust, pebbles, soil, sand… all sorts of things fall in. Add to that the debris brought in by swimmers: hair, skin flakes, etc. If the water chemistry is working properly, the remains of algae will also be present.

All this dirt has to be removed from the water; this task is performed by the sand filter system. Depending on the size of the filter tank, it is filled with 25 to 125 kg of the finest quartz sand. One-piece filter tanks should be filled to about two-thirds capacity, while the lower section of two-piece filter tanks should be filled to the brim. A proven grain size is 0.4 — 0.8 mm; the coarser the grain, the more small particles will pass through unfiltered.

The filter pump is also located on the filter tank. It draws pool water from the skimmer and the bottom jet and pumps it under pressure through the multiport valve into the filter tank. Inside the tank, the water rains down onto the quartz sand and seeps through. The fine sand retains most of the dirt particles. The cleaned water collects at the bottom of the tank, is then transported through very fine filter jets to the multiport valve, and finally returns to the pool via the inlet jets.

There is now much discussion about the length of the optimal filter runtime.

There are mathematicians who calculate filter runtime like this: the entire pool volume should pass through the filter system three times a day. According to this theory, the filter runtime for a pool with a volume of 30 cubic meters and a filter pump with a flow rate of 12 cubic meters per hour would be 7.5 hours daily. However, this calculation doesn’t take into account that the filter runtime needs to be extended at higher water temperatures. A better approach is this formula: half the water temperature equals the filter runtime in hours. Therefore, at a water temperature of 30°C, the filter runtime would be 15 hours. We take the middle ground between these two theories and recommend a filter runtime of approximately 10 hours per day for this pool volume.

The longer and better the water is filtered, the less water chemicals need to be added. And if the water doesn’t look perfect, we always increase the filter run time first before increasing the dosage of treatment products. With many years of experience managing a swimming pool in the garden, we can confidently recommend adequate filtration.

Pro Tip: Facing High Chlorine Demand in Pools in Glendale AZ? Our experts diagnose the cause, balance your pool chemicals, and restore clean, safe, and healthy water fast.

We often hear from customers that the filter runs for far too short a time because they don’t swim that often. Or the filter is switched off when the children are in the water. Some filters only run for a few hours at night. Or the pump runs for two hours, then takes a one-hour break, repeating this three times in a row. These intervals are simply damaging the electric motor of your filter system. And besides, everyone wants to save electricity.

Please don’t buy a pool if you want to save electricity. If you want to save petrol, you’d be better off taking the bus than putting tering around on the country road at 60 km/h – yes, sorry – that won’t work. There are now really economical filter pumps, but even they only work if you use them.

So far so good; however, at some point the top layer of sand, i.e., the largest filter surface, will become completely clogged. A pressure gauge is located on the filter tank, indicating the pressure inside. If the pressure rises by 0.1–0.2 bar, the filter should be cleaned.

The process is called backwashing and is very simple:

Switch off the filter pump (always!). Set the multiport valve selector lever to the backwash position. Switch on the filter pump. Run for approximately 2 minutes, or until the water in the sight glass is clear, depending on the pool size. Switch off the filter pump (always!). Set the multiport valve selector lever to the rinse position. Switch on the filter pump. Approximately 2-3 seconds should be sufficient. This cleans the filter piping of sand. Switch off the filter pump (always!). Now set the multiport valve selector lever back to the filter position.

During backwashing, the pool water is forced from the very bottom of the filter tank through the fine nozzles, rising through the sand to the top. All the dirt is flushed out of the sand and leaves the tank via the drain pipe.

While you’re at it, you should also clean the strainer in the pre-filter of the filter pump. To do this, close all ball valves and the multi-port valve, unscrew the cover ring, and remove the strainer. Even if it looks like there’s no dirt in the pre-filter strainer, it could actually be clogged with insects and other debris.

How often a filter needs to be cleaned by backwashing depends on several factors, but it should be done at least every 14 days. It’s also important to regularly loosen the filter sand; otherwise, the high pressure in the tank will eventually compress it too much, causing it to clump together. This creates channels through which the water can still pass, but the filter no longer provides any real filtration.

And believe us: If the multi-port valve is broken, the filter tank is cracked, or even the filter pump fails – we can clearly detect whether the valve has been switched while the filter pump is running. These are not damages covered by the warranty!

Last summer, a very dear customer came to us with a big problem: hardly any water was coming out of the inlet nozzles. When the diverter valve was in the circulating position, there was pressure at the inlet nozzles, but in the filtering position, almost nothing came out. I thought the customer had been caught: Aha – she hadn’t backwashed. But she assured me that she backwashed the filter weekly. Now, I’ve known the customer for a while and I know she doesn’t lie. So I kept racking my brains trying to figure out what the problem could be. I couldn’t find a solution or an explanation and was completely baffled.

Even people over 50 have flashes of inspiration now and then, so I had her explain exactly how she does the backwash. She rattled off her procedure like it was straight out of a textbook… right up to the 3-second time. 3 seconds? Backwashing for 3 seconds? Anja, you’ve got 100 kg of soaking wet sand in the filter tank and you’re backwashing for 3 seconds? In that time, the water can’t even get from the valve to the filter nozzles at the bottom of the tank, let alone all the way to the top through the entire sand filling, and pump the dirty water down the drain at the same time. She looked at me, dumbfounded, because the technician who installed her pool had given her precisely those instructions, and she’d followed them meticulously. When I explained to her what was actually happening in the filter tank, she burst out laughing, slapped me on the shoulder, and said that’s what happens when women believe everything men say without thinking. Bye – I really need to get home and backwash. It’s working – life can be so simple.

A similar phenomenon occurred at customer Carlo’s pool. The water flow from the inlet nozzles was barely perceptible. Again, I suspected the lack of backwashing, but no – everything had been done correctly. I stood in the equipment room, once again stumped. Then my gaze fell upon the check valve. The pool is situated on a beautiful property… right in the middle of the woods. Just to be on the safe side, I asked for a bucket and several cleaning rags and planned to open the check valve with a “ta-da!” Unfortunately, it was screwed on too tightly. With combined effort, the screw was finally loosened, and as soon as it was opened, the first beech nuts, leaves, and small stones tumbled out. I never would have thought that so much forest debris could fit into a check valve. After installation, the pool was first cleaned with the pool vacuum via the skimmer (to protect the cleaning robot – no joke), and all the construction debris, along with a lot of forest debris, was stuck in the poor valve. Forest out – water flowing – the afternoon at Carlo’s pool turned out to be quite enjoyable.

Enough filtration, the pool water still needs to be disinfected.

All sorts of life thrives in pool water. However, bacteria, germs, viruses, and algae have no place in hygienic water and must be removed. Chlorine offers a very reliable disinfection method; initially, it doesn’t matter in what form the chlorine is added to the pool water. We’ve dedicated a separate blog post to this topic . It’s important that the chlorine level remains consistently around 0.6 mg/L. In combination with UV disinfection, the chlorine level can be reduced even further to approximately 0.4 mg/L.

For the chlorine to be effective, an optimal pH level is essential. The pH should be between 7.0 and 7.2. If the pH rises to, for example, 8, the chlorine level would need to be around 3.0 to achieve the same disinfection effect as a 0.6/7.2 ratio. Whether the pH is regulated manually or automatically is irrelevant. Another frequently asked question is which pH adjuster is needed. In freshly filled water, the pH tends to rise. If it’s above 7.2, pH Minus is used to lower it. If the pH is falling, pH Plus is used. It’s best to refer to the packaging for dosage instructions, as these can vary depending on the product.

pH Minus lowers, pH Plus raises the pH value.

When summer starts to fade, we get a lot of pool owners coming to our pool center because their pool water has gone bad. It glows a lovely green from the jars. Even just opening the lid, you can smell that there’s hardly any chlorine in the water. Oh, right, you’re not using it as much now, so you can get away with being sloppy… nobody likes to hear that, I know; but that’s just how it is.

The same applies to water quality: the water doesn’t care whether you go swimming or not. If you’re careless with the water quality or filter runtime, your water will go bad in no time.