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Black Water

Is your pond going black? This is a sign that your pond needs attention.

29 August 2020

Why Is My Pond Water Black? (And How to Fix it) - Pond InformerKeeping ponds can be difficult; there are a variety of things for you to look out for, particularly the colour of the pond. The pond can be clear when it is fine, green when it is filled with algae, brown from tannins, foamy from excess proteins and decomposing waste, but it can also be black.

It is rare for a pond to go black in the summer months yet it can become more common in autumn; it can be a sign that there are several things in the pond that need remedying. Black water is normally caused by a chemical imbalance in the water or it could be a sign that there are longer term problems with the pond that would need to be fixed to prevent your pond from facing this problem in the future.

In most cases, black ponds can be caused by using a significant number of chemical treatments on your pond. Using treatments is normally fine and harmless, but using several treatments at the same time for a prolonged period can unsettle the ponds balance. Treatments should be used sparingly as a preventative measure, or in the appropriate dosage when problems are present.

Is this dangerous to Koi or Goldfish? Possibly. The black water itself is not harmful to the fish, but the underlying causes might be so you should investigate as soon as you see any colour change. Fish ponds should always have:

If your pond is black, you will need to investigate further to identify the cause. We have put some suggestions below with some solutions which should help to fix the black water.

Pond cleaningWaste or low Oxygen

This is the most common cause of black water in ponds. If your pond has a build up of sludge at the bottom, then it could be a sign that there aren’t enough healthy bacteria in the pond which can digest this sludge.

Normally, pondkeepers around the country will have a pump and filter system which can reduce the build up of waste, though you may need some assistance with this by using a vacuum or a net. A vacuum is often better at getting rid of the sludge, especially the PondXpert PondMaster (inc. Dirt Collector) deal. The dirt collector has a mesh inside of it which can help clean the pond more thoroughly, although a small amount of waste can be beneficial as it is an area where the bacteria will thrive.

The black water could also be down to a lack of aeration, as oxygen in the pond encourages the development of healthy bacteria which can digest waste in the pond and manage the Ammonia, Nitrite or Nitrate levels in the pond. Please see our blog on pond aeration to see if your pond has enough oxygen.

How To Repair A Leaking Pond | Midlands Pond ServicesDamaged Pondliner

A damaged pondliner can cause problems; the water levels will drop, this water can damage your underlay or ruin the ground around your pond. A damaged liner can also cause sediment and minerals to leak into your pond. This should cause your pond to go brown first, so if you see this, check out our brown water blog to identify if the brown water is caused by sediment first.

Green waterChemicals or algae?

The last reason the pond could turn black is down to a chemical imbalance in the pond from treatments or a bloom in algae growth. So please check that you are not using too many treatments. As stated earlier, use treatments sparingly when using them for preventative reasons; then follow the dosage on the treatments when problems are present in the pond.

If your pond has other chemicals in the water that could be causing problems, you should test your water thoroughly to determine the levels of Ammonia, Nitrite, Nitrate and PH of your water. You can do this by doing the following:

As always, if you have any queries, please contact us.

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