Q.  I have a black stain on the bottom of my swimming pool which appears to be getting bigger. A friend tells me it is algae; but I thought algae was green? Email enquiry, name and address supplied

A.  A common problem in swimming pools at this time of year is black algae; sometimes referred to as black spot Algae, explains James Lee. Often this type of algae will be found in tiled pools, particularly in the grouted areas and marbline pools.
Initially, ensure the filter(s) are clean and the pool is vacuum prior to any application of chemical treatment. Critically and often neglected, is the importance of lowering pH of pool water, ideally within 7.0 and 7.2, whilst treating black algae and brushing walls and floor surfaces. All algae cells have a waxy coating on the cell wall, so penetration of chemicals is made easier with a lower pH.
Assuming the swimming pool is sanitised with chlorine, shock dose the water with an unstabilised chlorine sanitiser – check pH balance after application of shock chlorine and adjust as necessary to 7.0 – 7.2.
Add a good quality black spot algicide; these products are specially designed to deal with the rigours of this specific strain of algae. In bad cases, it may take a few days for the stain to clear.
After the black algae has cleared, backwash filters, return pH to recommended reading o 7.4 – 7.5 and maintain correct sanitisation readings. It is also a good opportunity to take a sample of pool water to your local pool professional to check for phosphates. These nutrients provide the perfect environment for algae spores to thrive.

Q. I am confused by the various Lanthanum based phosphate removers available in the market place. Can you help? Pool builder, Essex

A. There are two main types of Lanthanum available for phosphate removal in swimming pools, advises Paul Grunhut. In areas of high phosphate when soluble ‘Lanthanum Salts’ are added to the water the Lanthanum will combine with the phosphates and the carbonate in the water which has a tendency to make it go cloudy.
There is therefore a need for a suitable flocculant in order to remove these, thus making the phosphate removal a twostage process. ‘Lanthanum Compounds’ avoid this problem and can provide continuous removal by coating the filter media.
In particular, soluble ‘Lanthanum Glycolate solutions which, when poured into the pool via the skimmer, are transported and retained by the filter.
In the filter, the particles dissolve and lanthanum carbonate forms on the filter media. This thin layer has a very high surface area and reacts specifically with phosphates, gradually transforming the layer into lanthanum phosphate for removal via backwashing to waste.

  

 

 

 

 

 Q. We have recently put a log cabin over our previously outdoor pool to increase use. Since then, the water quality is not as good as it was. The caretaker believes we need a larger circulation pump to speed up the filtration. Is he right? Head teacher, primary school, Somerset

A. Under no circumstances must you allow the caretaker to do what he is suggesting, warns Alan King. The increased suction and velocity through the pool bottom drains will cause a significant safety hazard to the children using the pool, with a risk of entrapment and drowning. You should seek advice on upgrading the filtration from a reputable professional swimming pool company. Meantime, ensure the careteaker has increased the frequency of backwashing and dilution to cope with the increase in bathing load and that he is using a flocculant (coagulant) to ensure the filter is working at maximum effectiveness.
The pool should not be used if it is not possible to clearly see the pool floor.

Q. I was asked to go to a site to measure for a liner on a home built concrete block wall pool. The screed floor was very rough, uneven, bowed and had craters in and the wall height was quite uneven. How do I fit a liner to this? Pool builder, Northumberland

A. Firstly, talk to your client and advise him that due to the quality of the screed you cannot guarantee a perfect fit, suggests David Dahl. He then has the opportunity to do some remedial work to the screed and the pool can be measured again.
If the client wants to go ahead then talk to your liner manufacturer and send him a copy of the drawing and photos if possible, they may well make some good suggestions.
It should be possible to get a reasonable fit by making the liner a little smaller than normal and stretching it in. You just have to work out where you can afford to take the material from in order to get stretch where you need it.
It may even be better to choose a 20 thou liner as it is easier to stretch it in.

Q. In the last couple of spa tests, I have had readings of Pseudomona – 12 one month and 19 CFU last month. Is this an area for concern? Holiday park operator, South West England

A. Well-operated pools should not have a presence of Pseudomona, comments Allen Wilson. If the amount rises about 50 cfu/100ml; you should temporary close the facility.
The inside of pipes and balance tanks provide bio-films on the interior surface that bacteria can breed and hide in. This is why it is so important to brush balance tanks. We cannot get inside the pipe work to physically clean. I would seriously consider a cleaning regime involving controlled used of chlorine dioxide on a regular basis.
Another grim possibility is that they are growing inside the filter but again after using the chlorine dioxide, backwash the spa empty via the filters.
Remove the eyeball type water jet inlets and physically clean and disinfect.
Don’t forget, every third month you should also have attest carried out for the presence of Legionella. Last, but not least, invest in some site-specific, meaningful training. Good control of disinfectant and pH, good backwashing and housekeeping techniques.