Category Archives: Swimming pools

How to get rid of black algae

Black algae attack – how I got rid of it some years ago:

Here’s an unedited entry from my diary in July 2007 when I had black algae outbreak in a 10×5 metre pool of classic tiled concrete construction:

“With pump off, I brushed off every bit of black algae that I could see. This took more than 3 hours of hard scrubbing. Whilst doing so I dropped shock chlorine onto the floor in the position where I was working and also used a chlorine tablet on the bottom of the pool, which I placed over really stubborn marks after brushing them. I then went back to the stubborn marks and brushed again until it was all gone. In total I put in 20g/cubic metre 1.5kg in total into the 75 m3 pool. This should have raised the level of free Cl to about 20 ppm (I hope).
The water, incidentally, was crystal clear prior to and during this operation. I found a small reservoir of algae hiding in a skimmer flap. Between the flap and the float chamber was a layer of black algae, this was cleaned and disinfected.
I then vacuumed the pool to waste. I put 4 Cl tablets into the floating dispenser and fully opened the water vents for maximum dispersal.
I am now running the pool pump for 24 hours continuously.
Tomorrow I will check for algae growth and probably vacuum to waste again.”

This did get rid of the black algae, but it is very difficult to eradicate. Eventually the installation of a salt water chlorination system kept it from forming again. I hope this is helpful to anyone battling black algae which normally tries to take root in the grout of tiled pools. Fibre glass pools are not usually so badly affected.

Page reviewed 31 August 2017

Ten important points about swimming pool maintenance

Pool maintenance is about plumbing, water chemistry and common sense. Listed below are 10 important things about looking after your swimming pool:

1. Most problems are caused by incorrect pH. pH is the acidity balance. Use a testing kit. A pH of 7 is neutral, 8 is alkaline, and 6 is acidic. Pools should be maintained at pH 7.2
As this is the most important thing, make sure that you adjust your pool to the correct pH. If your pH is above 7.4 ad pH- (which is an acid). If your pH is below 7.0 ad pH+ (which is an alkali). Chlorine does not work very well when the pool pH is too high and algae can more easily grow.
When adding chemicals first add them to water in a bucket to dissolve them, then add to the pool slowly at the inlets with the pump on.
Always follow the instructions on packs – pool chemicals are potentially dangerous.

2. The next most important thing is maintaining the correct amount of free chlorine in the water. It should be 1.5 ppm (parts per million) but a value between 1 and 3 ppm is OK. If there is no chlorine detected with your testing kit, the pool is not safe to swim. If there is no chlorine at all in the pool immediately add 10 grams of shock dose (granulated or powdered chlorine) per cubic metre of water. For an 8m x 4m pool, this would be about 450 grams. Add it to the skimmers while the pump is running, and leave it running for at least 4 hours.

3. Twice weekly checks are important. A pool should not be left without any maintenance for long periods. Checks should be for chlorine and pH levels and adjustments should be made. Keep the pool topped up – half way up the skimmer mouths is the correct level. If the pool gets too low it can suck air, annoying your neighbours with the noise, and possible damaging your pump impellers.

4. Once a week, vacuum the bottom of the pool, and brush the sides to remove all dust, soil and any slight algae growth. A well maintained pool should not grow algae, but we all lapse sometimes! Keeping your pool clean means that less chlorine is required to maintain sanitisation.

5. Deal with algae growth immediately! If your pool starts to turn green, get on top of the problem. Ensure the pH is at 7.2. Add 15 grams of shock dose chlorine to the skimmers for each cubic metre of water. This is about 700 grams for an 8m x 4m pool. Add it to the skimmers with the pump running. Hoover the pool and brush the sides and ensure that daily checks are made until the problem has definitely been cleared.

6. Do not add chlorine tablets to the skimmers. Use a floating chlorine dispenser. This helps to protects the skimmer area and associated pipework from extremely high chlorine levels which can damage the pipework.

7. Once a week in the summer months only, when the pool is above 18ºC add 450ml of liquid algicide to an 8m x 4m pool (approx 10ml per cubic metre). This will help to keep algae at bay.
NOTE: Different makes of algicide have different concentrations so check the instructions.

8. For safety reasons, it is best to never bathe alone. It is also imperative that young children are not allowed unrestricted access to pool areas. Sadly there are many cases of drowning in pools in Spain every year.
It is recommended that you do not bathe in the pool until 2 hours has elapsed after adding chemicals.

9. Remember that once the pressure on the sand filter dial reaches the yellow area, the filter needs to be backwashed. To do this, turn off the pump. Then move the multi-port valve to backwash. Run the pump for the time suggested in the filter manual. Usually 90 seconds or until the waste runs clear (if you can see it). Then stop the pump change the valve to rinse and run for 30 seconds. Always stop the pump before changing the multi-valve positions.

10. If you have difficulty with your pool call in an expert. Your pool is worth a lot of money and sometimes you need to spend a little on extra help.
Most of all, enjoy your pool and stay safe!

Salt water chlorination versus conventional chlorine swimming pools

Salt water pool chlorination?

I have the responsibility of two swimming pools and I thought I’d share some thoughts regarding salt water chlorination.

Pool 1:
We took possession of our first pool in 1999: a 10×5 metre pool which had traditional treatment and was only 1 year old. I managed it without too much of a problem until 2007 when it had a black algae attack. This was dealt with but returned each year.
In 2011 we decided to have an Astral Sel 100 salt water chlorination system fitted to this pool, which cost about €1,150. This worked very well, in fact the chlorine production was very efficient, it completely eliminated any trace of black algae and we have never seen it again. The pool is now 14+ years old.
BUT: The control unit has recently gone wrong and has been examined by a local electronics expert and is unrepairable due to ingress of “a corrosive liquid”. The unit was installed professionally in a dry underground pump house, and was only 2.5 years old.

Pool 2:
Installed 2003, 8×4 metre polyester insert supplied with a free Osec OS-3 self cleaning (South African) salt water system. This functioned well only until 2005, when the cell failed. The replacement cost around €400 including import taxes from South Africa. The cell failed again in April this year when I decided to abandon salt water chlorination in that pool. The cells were discarded, but the control unit was still working.

I have now placed the old Osec control unit from Pool 2 onto the Astral cells at Pool 1, and it seems to be working. When either the unit or cells fail, I will probably abandon salt water chlorination at Pool 1.
I used to be a supporter of salt water systems but now I’m moving away from that position.

Advantages of salt-water chlorination systems:
Easy maintenance and less maintenance when the system is working correctly.
No necessity to handle chlorine tablets or powder which are very unpleasant and toxic.
The salt-water is said to be better for people’s skin.
Less likelihood of a pool crisis through neglect, stays stable for longer.

Disadvantages of salt-water chlorination systems:
Very costly initial installation, and repairs when they are needed.
Short cell life, they are guaranteed for 2 years, but may last 3 years or up to 7 years if you are very lucky. Cell replacement is €400 – €500 if you do it yourself.
Extra electricity bills, as it is necessary to run the system for much longer per day, than a conventional pool, to maintain the chlorine levels.

I don’t think there is a clear winner in the salt-water/chlorine debate.
A salt-water system will probably pay for itself in 3-4 years, as no chlorine products should need to be purchased. Some salt will be required but it is very cheap to throw in a few 25 kg bags to top up the concentration.
Pool salt should be about 4 grams per litre (0.4%) so for an 8 x 4 metre pool with 40 cubic metres (40,000 litres of water) 160 kg of salt will be required initially, if converting the pool.

Swimming Pool temperatures in Arboleas, Almería, Spain

I’ve just been looking at past pool temperatures, over the last 6 years and these are the averages.
The swimming pool is uncovered, unheated, about 8m x 4m, and 1.5 metres deep.
Temperatures in degrees Centigrade (Fahrenheit)

January – 9 (48)
February – 11.5 (53)
March – 13 (55)
April – 18.5 (65)
May – 20.5 (69)
June – 25.5 (78)
July – 28 (82)
August – 27 (81)
September – 23 (73)
October – 18.5 (65)
November – 14 (57)
December – 10 (50)