Algae is a pest to most aquarium and pond owners, it's unsightly, potentially harmful and is probably the main cause of why people leave the hobby.

Algae is an aquatic organism that uses photosynthesis to grow, much like plants. Whilst algae is natural, and in most cases absolutely fine, in fish tanks it can make the tank look dirty and if water conditions are unbalanced can produce algae blooms, which can create harmful conditions. These blooms, and general fast growth, is usually caused by light, organic waste build up , Phosphate & unstable water conditions.

The more light in your tank, the less ammonia is needed to produce algae growth so finding the source of ammonia is key to keeping your algae levels down. This can be a number of things but the most common tends to be overfeeding, a poorly maintained filter, a filter that's too small and a dead plant or fish. 

Although chemical treatments can work for a time, it's important to address the root cause so you’re not repeating this process forever!

For algae types and ways to get rid of specifics delve into it here:

Diatoms

Problematic during aquarium start ups when it tends to flourish, a slime like algae that is caused by ammonia and silicates. Increase lighting and wipe away the brown film, it’ll go away soon enough.

Green Water

A single celled, free floating algae that cannot be eradicated by water changes. Usually caused by excess nutrients in tanks with poor flow and circulation. Methods to get rid of it include using a UV clarifier, using a treatment thats binds it together or turning the lights off and covering in a dark sheet for a number of days can also work.

Blanketweed

A form of algae that is normally a problem in ponds but can find its way into aquariums. Long candy floss strands that grow very large and fast and can even trap fish in extreme cases. As with most algae, keeping nutrient content low and reducing lighting to prevent its growth, but once its there, physical removal is a must and in ponds using a product like blanketweed balance, Kusuri EcoPure, Kusuri Gold or barley straw will help keep it at bay.

Blackbrush

A real nuisance algae that starts as small hairy tufts here and there but can quickly overwhelm surfaces. Its common cause is a lack of carbon dioxide, high lighting and/ or poor flow in the tank. It's not really eaten by anything and treatments have little effect so physical removal of it out of the tank is the only option if it appears (don’t let it float around the tank).

Staghorn

An ugly type of algae that usually starts high up in the tank as it tends to bloom when light levels are high but will work its way down and smother things soon enough. As per usual, poor nutrient levels and low flow will also add to this algaes growth. Check your filter is working properly and maybe make water changes happen more regularly if you are seeing this happen more.

Green Fuzz

Looks similar to staghorn at first but has smaller threads and tends to prefer infesting plants. Normally gets a foothold on dead or dying plants that need some much needed pruning alongside the usual suspects of poor nutrients, low carbon dioxide and low flow. Remove the dead plant matter and increasing CO2 is recommended.

Green Thread

A common algae that is particularly bad for moss as it tends to work its way deep down and is very difficult to remove. It has no proven cause other than the usual things mentioned plus anecdotal reports of high iron levels found in substrate and fertilising tablets. Thankfully it is easily taken care of by fish, such as siamese algae eaters, and amano shrimps but best to snip it off it takes hold.

Green Spot

A very common sight in tanks, especially established ones. Small spots that usually appear quite dark and can appear anywhere but are commonly seen on the glass and can really affect slow growing, larger leaf plants if you have them. Caused by high levels of lighting and poor nutrients such as phosphate, reducing light levels by 40% and removing it with an algae pad or old toothbrush… however, it is quite stubborn to get off!

Green dust

Another common algae that is part of most aquariums that aren’t dedicated aquascapes and appears as a green slime across the glass. Low CO2 levels and a lack of plant food are the main culprits but it's easy enough to wipe away and fish such as bristlenose catfish can keep most at bay.