The warm weather has arrived and pond season is upon us. But while the garden is likely to bring us joy in the summer months, a polluted pond would soon cast a grey cloud over things.

But how do you know if your pond is polluted?

One way is by the behaviour of the fish. They will often grasp at the surface or lie motionless – ion which case you need to break out the test kits. Test regularly for ammonia, nitrite, nitrate and pH.

If you detect nitrite then you ought to increase aeration by ensuring that fountains, pumps and waterfalls are left running continuously. Nitrite reduces oxygen – so you have to put it back in.

Food can also create pollution – so make sure you limit feed to a bare minimum.

Large water changes should also be carried out to dilute the concentration of nitrite in the water. Use the pump to remove 25-50% of the water each time. Top up the pond using a hose, but don't forget to dechlorinate the water to neutralise the chlorine or chloramine present.

Salt is excellent for reducing the toxicity of nitrite without the fish falling ill. Follow manufacturer guidelines.

Testing pH is also vital. The actual amount of toxic free-ammonia present depends on the pH and temperature of the pond water. So you need to test the pH and temperature to find out how dangerous conditions are for the fish.

One of the premier pond test kits our experts recommend is the Oase Water Quality Master Test Kit.

This kit gives you a full range of test materials and equipment. It tests all the above levels, like pH, nitrite, nitrate and ammonia as well as total hardness, carbonate hardness and phosphate levels.

For a more futuristic solution, consider the Seneye Pond. This is an electronic device that will actually report back to you by texting or emailing you with the levels inside your pond.

And this software doesn't just give you statistics, it also gives you advice on dealing with the problem.