Recheck the test, if the tablet stays white and the water is clear when the tablet has dissolved then the chlorine in the swimming pool has been used up, however if the tablet turns speckled pink but still dissolves clear then the high level of chlorine has bleached out the test. Recheck the test, diluting the sample with tap water and multiplying the result by the dilution rate.

The heat retention blanket should fit with the bubbles downward, this ensures that there is an even insulation gap between the swimming pool water and the air above. If you've got it the wrong way up it will still prevent most of the heat loss by evaporation.

This is a large subject and you may have to involve your local swimming pool company. Some investigations by yourself will help you and your service agent get to the solution more quickly.

Check if the multi-port valve is leaking to waste. Undo the union on the waste line and run the swimming pool pump, or check the outlet of the waste pipe. If water is dribbling from that pipe when the valve is set to "filter" you probably need a new valve.

Check if the pool leaks more with the pump running, less or the same. This could indicate pressure pipes, suction pipes, or the pool fittings or shell.

Make a note of any gardening or fencing work done near the swimming pool or in line with the pool equipment room.

Note how much water you lose when backwashing.

Check for cracks around plastic swimming pool fittings particularly the skimmers.

Check for subsidence around the pool and damp areas of garden.

Note if the swimming pool level has dropped below all the fittings except the main drain (sump). It could be the hydrostatic pressure relief valve leaking. Many swimming pools have a sprung valve in the sump which lets ground water into the swimming pool if the level of water in the pool is pumped lower than the water table around the pool. This prevents the swimming pool floating on the water table.

If you haven't solved the problem yourself by now let the pool company have this information. It could save them time and you money.

The swimming pool heater will only work when the pump is running, extending the running time (And if the heater has a timer extend that time too) . Check that the heater thermostat is turned up enough and that the filter has been backwashed (If the filter is blocked the pressure switch in the heater will not switch on).

Make sure the bubble cover is put back on the pool whenever the pool is not in use.

Have the swimming pool heater serviced every year. This needs to be by a CORGI registered gas technician who has been trained and licensed for your particular type of heater. When booking tell them the make of heater and ask if they are qualified for that particular one. Ask about an out of season discount.

Check that your swimming pool isn't leaking. If you have an automatic filler, check that it isn't running all the time. It is not unknown for these to be installed because a pool is leaking so the leak will not be noticed. It's your hot water running away.

Your summer cover is reaching the end of its life and the bubbles are breaking up and clogging your system. This happens to heat retention covers eventually but you can slow down the breakdown and extend its life.

Always cover the summer cover with a white plastic sheet when it is rolled up on the side of the swimming pool. This helps to prevent the suns rays forming heat inside the cover and breaking down the plastic. Many suppliers provide a plastic cover with the heat blanket.

When you super-chlorinate the swimming pool, leave the heat blanket off the swimming pool until the chlorine level is back down to a normal level. The chlorine can bleach and harden the bubbles making them brittle.

Yes, normally about every 5-7 years. The sand starts to cake from the outside of the tank inwards reducing the effective filter area. Commercial swimming pools often have the sand part changed several times a year and fully changed each year. These are often treated with sanitizers to kill off any bacteria growing inside which could spread to the pool and cause a health hazard.

Check with the filter manufacturers instructions on their recommended method and media for your filter. Most filters are sand based though some sand filters are filled with Zeolite which is a micro-porous volcanic material acting as a finer filter than sand.

Changing the sand is straightforward if a little laborious. If you do it yourself, make sure that the 'O' ring seal is available in case your old one doesn't reseal. The process is simply to take off the lid ( A tool can be obtained through your local pool shop), remove any top pipe work, dig out by hand or vacuum out all the old sand and pour in the new. Check with your pool shop how much sand your make and size of filter holds and buy only graded filter sand. Some helpful pointers are listed below.

Don't disturb the thin black tube sticking through to the top of the filter. This is an air bleed tube and is the only way out for air trapped in the top of the filter tank.

Be careful when digging the sand out from the bottom of the filter to avoid damaging the laterals. These are thin tubes with slits which allow the passage of water but not sand. If they are damaged the sand will be pumped through the system into the pool.

When refilling the filter put some water in first. This stops the sand settling in piles on top of the laterals and damaging them.

Protect the filter top threads from getting sand in them by installing a polythene bag, with the base opened, over the threads and another over the top pipe to prevent sand entering the pipe work to the multiport valve.

If the filter has a multiport valve which screws straight into the top of the tank the you'll need a special tool which protects the thread and the pipe, and holds the pipe central to the tank. This is necessary to allow the valve to screw down.

Last but not least, backwash all the dust out of the sand before setting the multi-port valve back to filter.

In 99 swimming pools out of a hundred, the under water bulb can be changed with the swimming pool full. The lamp assembly is screwed or clipped into a housing fixed to the swimming pool wall and, when unclipped or unscrewed, will reach the top of the swimming pool on an umbilical cable.

Once the waterproof assembly is on the patio it can be simply unscrewed, the old bulb and o ring removed, the terminals cleaned, the new bulb and o ring fitted and the assembly screwed back together.

The excess cable is then wound round the assembly as it is lowered back into the swimming pool and is clipped or screwed back into its mounting in the swimming pool wall.

Check the deck box terminals. The deck box is a small plastic or metal junction box on the patio above the light which houses the joint between the cable coming up through a conduit from the light and the cable coming from the transformer (most under water pool lights are 12 volts to eliminate any danger if in contact with the water). This junction can become corroded and should be replaced in the event of signs of rust or heat damage.

The lives of light bulbs are notoriously varied but checking the look of a failed lamp can give some indication of its demise.

1. If the bulb has turned black this indicates an electrical problem.
2. If the bulb has turned blue this suggests water ingress.
3. If the bulb has turned white it usually has just worn out.

With an electrical fault an electrician should be consulted. Water ingress requires careful replacement of the o ring seal and checking the cable gland for wear and checking for heat damage of the assembly.

New under water light "guts" can be purchased which consist of the detachable part of the light fitting (with the bulb inside) and cable. Do consult your swimming pool shop about fitting this unit and remember to pull a draw string through when removing the old one.

Try setting the multiport valve to re-circulate and checking the pressure with the filter out of the formula. If the pressure is still high then you may have either a blocked heat exchanger in the gas heater or the bypass in the header has jammed or the non-return valve at the base of the heat-sink is jamming part closed. If the pressure drops to the normal or lower when on that position it suggests that the sand is "caked" and needs changing, or at least the filter lid taken off and the sand given a good stir (careful not to damage the laterals though). Has anyone done any patio repairs where cement could have got into the pool. Cement has a habit of setting especially when mixed with filter sand.

Anyway, there is a start to your investigation.

Sand in the swimming pool is indicative of a lateral broken or misshapen or the air bleed tube coming adrift. The sand in these cases drops out of the return jets and forms a pile below. If you sweep it, it moves a bit but stays where it is swept to. When refilling the filter with sand, part fill it with water to prevent the sand settling on a lateral and bending or breaking it. See previous question and answer

Dead algae, which looks like sand, will, when brushed, disappear into the water, only to settle later in a similar position. Even if you vacuum it through the filter it will pass through the sand and again re-appear in all the old familiar places later. the solution is to vacuum it to waste (vacuum with the multiport valve set to the waste position, the vacuumed water then goes straight out of the waste pipe and not through the filter) You will lose around 6" (15cm) of water.