doubt we have ever had a customer here at Bradshaws Direct that hasn’t suffered at some point along the way with some form of green water, algae or blanketweed problem. The reason behind this is that we change a pond to suit our own personal needs, we reduce the amount of plants, add lots of fish and oxygen - giving the perfect conditions for the dreaded algae to flourish.

Algae is very much part and parcel of the make up of any pond, it is a single-celled organism which grows, breaths and photosynthesises. This would normally go unnoticed; however some species can join together to make structures that can only be viewed under a microscope, therefore giving your pond a green tinge.

Algae is a term that is used to cover numerous different species of usually single-celled green plants that are found living in water. There are calculated to be over 15,000 species of algae in Britain alone! Some of these will form together to make large plants, for example silkweed - which is actually a colony of single-celled plants that happen to grow together.

In the pond world we would usually group these together under two main categories, ‘Green Water’ and ‘Blanketweed’. Blanketweed is a colonial algae, here single cells join end to end forming long strings that make up the ‘blanket’. Planktonic algae are however grouped together under the ‘Green Water’ Category. What do we mean by Planktonic? Planktonic means that they are free-floating in the water column rather than attaching themselves to rocks, plants, Liners etc. (Firestone Liners have a special property to prevent this from happening, a story for another time!).

Spring and summer are the worst time for Algae in a pond, your fish will be feeding well and constantly adding to the supply of nutrients that are going into the pond. In these conditions, algae can reproduce at an alarming rate, with each single cell being able to replicate itself once in a 24-hour period. This is called an Algal bloom and it can quickly take over and become a problem for the health of your pond life if it is left untreated. Only one species of algae will usually take over at a time, so if you have green water you generally won’t suffer from blanketweed, and vice versa.

Why is algae harmful then? Well this is because of the depletion of oxygen. In a normal nature pond, fish stock levels are low and oxygen levels are not an issue. During the day algae will produce more oxygen than it uses, however at night when there is no photosynthesis the huge number of algal cells will be using all the oxygen for respiration. During these blooms it isn’t uncommon for the algae to use nearly all of the oxygen within a pond, so if you are checking oxygen levels in your pond you need to do this at different times of the day.

Algal blooms can also be a nightmare for us fish keepers and the equipment that we use. They can block and clog pumps and filters and affect the whole filtration system. I would like to point out that algae has no actual water quality detriments apart from the oxygen levels as discussed, we just need to know how to manage it better when blooms happen. My next blog will touch on treating green water, algae and blanketweed problems, so stay tuned for that.