Algae Growth in Marine Aquaria

Algae Growth in Marine Aquaria

This month’s topic is one that a lot of customers are asking us about – and that is algae growth in the aquarium.

The answer to this is not always simple – but there are a few simple checks that you can make to help find out the cause.


Nitrate should be as low as possible – but in our humble opinion not zero – some creatures, like anemones, clams and micro algae need nitrate to feed on and ultimately stay alive.


Phosphate should be as low as possible – and if you can achieve it, zero.


Check the calcium level – it should stay at 420 ppm and remain stable, if it fluctuates this can cause problems.


Ph must also remain stable at 8.2.

Weekly tests are a must – but let’s be honest, do we all do this? Most of the time the readings are correct – but the time we don’t test is when problems occur.

A quick tip – if your test kits are over six months old the reagents will have oxidized and will not give correct readings.


Maintenance is the key – when we keep tropical aquaria we use a gravel cleaner and keep the substrate spotless. Most marine keepers don’t use this but it is a great tool for getting muck out of the sand and always pay attention to those dead spots.

If you have never used one before, you’ll be surprised at how much fine brown dust comes out of the sand – particularly next to the live rock, this mulm is a major cause of phosphate.

So clean the tank, do a 10% water change weekly, clean your filter (in water taken from the tank to preserve the bacteria) and keep your protein skimmer clean to maximise its efficiency.

If you need to, add nitrate removers like Seachem’s de-nitrate and change it regularly. For high phosphate use Phosguard or Rowaphos – these are best used in reactors but work well in filters.

Turbo snails will keep algae down – and for tanks that have a lot of algae, particularly hairy growths, a sea hare is a super addition to the aquarium – not the prettiest thing in the world (see picture) but it will demolish algae!


Lighting also plays a part, fluorescent tubes last twelve months after this time they have lost 90% of their output!

Although they still look bright to us, they aren’t to the creatures in your aquarium. Old light tubes give the wrong spectrum of light and will lead to excessive algae growth.

Leave your lights on for eight to ten hours daily.

With a little extra care we all can have a happy aquarium!

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