There are at least six different types of cloudiness of your pond water, and they each have a different cause and solution.
- Green Water
- Brown Particulate Cloudiness
- Brown Tint, like Iced Tea
- White Cloudiness
- Greyish Cloudiness
Let’s address the last one of these first. #6. This cloudiness is typical of a brand new pond and just means that no matter how well you think you washed those rocks, you didn’t get all of the mud and silt off of them. What to do? Nothing. Wait anywhere from a few days to a few weeks and the filter will trap all of this. Don’t waste your time / money trying to speed it up with chemicals, this is inorganic sediment and those “clear the pond fast” chemicals are for organics. Sit, have a drink and wait. Or do a bunch of water changes.
Next, #1. Green Water. Green water is microscopic algae floating in your water, making it look like the water has been dyed green, or in bad cases, like pea soup. The absolute best fix is to install an Ultraviolet light in your system. The light must be correctly sized to both your pond and your pump. If you have a UV light and your water is still green, either your light is too small for the pond, too small for the pump, your bulb is too old (the bulbs are only effective for one year – they will come on and glow for much longer, but after about twelve months they are no longer strong enough to kill the algae) or you got a cheap Chinese made bulb, most of which are very ineffective. Lacking a UV light, the next best solution is to use either barley liquid or pellets combined with lots of plants. The barley products inhibit algae growth and the plants outcompete the algae for nutrients and starve it to death. Third and fourth solutions would be either barley products or plants by themselves. Last, and highly discouraged solution is a liquid algaecide. Liquid algaecides kill quickly but do not remain in the water. Killing too much algae too quickly can result in a lack of oxygen in the water that can kill your fish. Additionally, new algae spores land from the air and start growing the next day, and algae can double in volume every six hours.
#2. Brown Particulate Cloudiness. Particulate cloudiness is caused by insufficient, inefficient, or overloaded filtration systems. Keep in mind that most manufacturers seriously over-rate their systems. Assuming an adequate system, temporary overloads can be caused by overfeeding (you must cut back on feeding at both very high and very low temperatures), cleaning your filter at the wrong time (early spring and late fall ONLY) as cleaning sets your filter back by several weeks, not adding beneficial bacteria to the system regularly or inefficient water flow not taking debris to the filter. This last can usually be remedied by adding airstones / aeration and / or relocating the pump.
#3. Brown Iced Tea like Tint. Iced tea water is the result of tannic acid discoloring the water. It is caused by leaves and similar debris in the water breaking down. Any leaves, sticks and branches should be kept out of the pond or removed as soon as possible. All woody plant leaves are bad, but green leaves are worse than dried leaves, pine needles and oak leaves are particularly bad and acorns are the worst. This condition will go away on its own, but it may take months to do so. Activated charcoal in the filter stream will remove it, or a water change.
#4. White Cloudiness. White cloudiness is usually caused by a bacterial bloom in the water and as such seldom lasts long and is frequently self-correcting. Adding a mild anti-bacterial such as Melafix will help.
#5. Grey Cloudiness. Grey cloudiness is generally from an elevated phosphate level in the water and can be corrected with either a water change or a chemical to lower the phosphate level. Always test the phosphate level first to confirm before treating though. Elevated phosphates can come from overfeeding, overcrowding, inefficient filtering or simply be present in your source water.