All that bubbly white or gray buildup is likely to be caused by an excess of organic matter in the water. Accumulation occurs when there are too many fish living in the pond, you are overfeeding them, the filtration is inadequate, or there is runoff seeping into your water garden. Bubbles in your pond can be caused by a number of different causes. If you see bubbles in your pond, it could mean that your liner or pump requires maintenance, or it could indicate that the filter is clogged.
By eliminating some possible causes of bubbles, you can better understand what the cause may be and start taking steps to eliminate the source. Gas pockets naturally form in the substrate of all waters. Having a lot of foam often means you have too much organic material in your pond and your populations of beneficial bacteria can't break them down efficiently. Pond skimmers are especially useful for reducing organic material that swims freely, as they often come with dedicated filter media that provide additional biological filtration.
While you get to the root cause of the foam, you can make weekly water changes to improve the appearance of the pond if it becomes a problem. That's why adding bacteria to reverse this process is useful and can help prevent the pond from aging prematurely. This unsightly foam is very common in spring, when the pond balance is not yet set for the season. Defoamers are a very quick method of removing frothy water and preventing it from returning for a short period of time, so they can be useful in improving the appearance of the pond while solving any underlying problems.
Overfeeding fish or using a low-quality food with too much “filling” can contribute to the formation of frothy water, both of which can cause organic material to build up in the pond. In fact, protein skimmers designed for large ponds can be extremely expensive and very complicated to install, so we only recommend them for ponds with large stocks, breeders, or to complement a normal skimmer and filter configuration. Finally, you'll want to make sure your pond is free of algae, as they're packed with organic material that dissolves in the pond when they bloom and die. An excellent method to remove foam from surface water and prevent floating debris from adding to organic material in the pond is to install a water skimmer.
Even in fishless ponds, you'll still see foam appear, especially if you have waterfalls, fountains, or live in windy conditions. The best way to know if you have a water quality problem is to test your pond with a wide-range water analysis kit that provides measurements of elements such as ammonia, nitrites, pH and kH (alkalinity).