Problem Algae in the Marine Aquarium

By Richard Webber

When you talk about algae in the marine aquarium, you are most likely talking about 'problem algae' (micro-algae) rather than the 'plants' (macro-algae) that look good in the aquarium. This article is a look at controlling problem algae in your marine aquarium. It is purposefully brief, and is aimed primarily at 'fighting the fire'. A longer in-depth article does exist called 'Marine Algae Overview' that has a lot more information on algae and its use in a marine aquarium.

There are three types of algae, in order, that I consider problem algae. These algae are going to find their way into your tank. Their spores will reach your tank from the air or from the water your livestock or foods come in. You cant stop them getting into your tank.

Hair algae

This grows in mats, and looks like fine hair (thus the name), it can grow over rocks, other substrate, glass, pumps, pipes - basically anything in the tank.

Slime algae

This is a greasy alga in red, green or black varieties. It covers rocks and substrate.

Diatomic algae

Is very fast growing brown film that grows on the glass especially in aquariums with strong lighting.

There is never a single causal component to algae affecting an aquarium. Rather, it is a combination of factors. These include water quality (phosphates, nitrates & ammonias), accumulation of detritus, lighting, and supplements.

Phosphates: Any measurable level of phosphate can cause algae problems, as it is a primary food source for the algae. Levels of phosphate should be kept as low as possible.

Nitrate: Is another food source for algae.

Ammonia: Algae can take up ammonia directly from the water.

Detritus build up: Pockets of sediment are often the first place algae get footholds. Hair algae specifically seem to 'trap' detritus and then utilize this for further growth.

Lighting: Bright lights with a long photoperiod will help algae grow. Additionally old lights shift to the red end of the light spectrum as they age, encouraging algal growth.

Supplements: Only use supplements if you are sure that they will benefit your aquarium inhabitants.

A combination of the above is the likely cause of your algae problems.

How to get rid of problem algae

Once you realize you have an algae problem, things need sorting out as fast as possible. The problem will not go away as quickly as it arrived, but you can keep it under control.

What are you putting into your tank? Check to see if you can reduce the food you are adding to the tank. Eaten and uneaten food becomes algae food! Check the quality of your food. Are you dumping a frozen cube into the tank? A lot of the cube is 'dirty' water and bits of shrimp that the seahorses will not eat, but immediately becomes a food source for the algae. Rinsing the food will reduce the effluent from fouling the water.

First, start the mechanical removal of as much algae as you can get your hands on. This is the initial major clean up. During this time it will help to add filter floss or filter wool as the first stage in your filter - to capture the pieces of algae dislodged by your clean up, but not removed from the water. Make sure you clean or replace this filter regularly in the first few days. Check the condition of your filter at the same time and clean as needed.

Next, check your water flow. See if there are any 'dead-water' areas, in which algae can get a foothold.

Vacuum the substrate to remove as much detritus as possible. The water removed from the tank should be replaced with new seawater from a source that does not contain phosphates or nitrates, such as reverse osmosis (RO) water. A 20% water change is most beneficial.

If your photoperiod is more than 12 hours, consider lessening it. Replace any bulbs over six months old as the spectrum emitted shifts over time to light emissions that promotes algae growth.

Now attempt to improve the water quality. Adding commercial products to the filter is the first line of attack to improving the water quality quickly:

Polyfilter - Available as a pad. You can cut it to shape to fit your filter. Add the Polyfilter as the LAST stage in the filter - before the water returns to the tank. Polyfilter removes dissolved organics, minerals as well as some phosphates and nitrates.

Phosphate remover - There are several commercial products available to remove phosphate from the water. Most are in the form of a powder which is added to a filter. Place this second last in the filter, before the Polyfilter. You have to be cautious, as some types leach the phosphate back into the water after removing it. Read the instructions! I use Rowaphos which is the best product I know of for removing phosphate. This product also reduces silicate - which is a contributing cause to Diatomic algae.

Next thing to consider is the 'cleaning crew' or animals that eat/control alga. Dumping a cleanup crew into the tank is not an answer by itself. They will not be able to deal with an outbreak caused by poor maintenance, and most cannot deal with established algae problems. They are however a useful tool in the ongoing control of problem algae. I follow the general recommendation of one red leg hermit and one turbo or astrea snail per five gallons of aquarium water. Having cleaned the major patches of algae out of your tank, your cleanup crew should be able to assist in keeping any future outbreaks under control.

Lights are a problem area. If you have corals, you will need the lights, but if you have a fish only tank, you can turn off the lights for a few days. The fish will not mind, accepting the ambient light, but the algae will not be happy. Even tanks with corals can do with a break from the lights. If you have corals try reducing the photoperiod.

Finally, Macro-Algae - using algae to control algae! Macro algae is the 'plant' and encrusting algae that you see in marine tanks. Macro algae cut down on light available to the micro algae, and compete directly for the nutrients otherwise available to problem algae. Caulerpa spp and encrusting corallines (a group of Red algae resembling corals) are best. Encrusting corallines produce chemicals that stop the growth of micro-algae on rocks etc. Caulerpa is a fast growing green macro-algae, and commonly available.

Another less commonly used method is that of mangrove plants, whose roots extract the nutrients micro-algae would need for growth. These however take several months to become effective, and success stories vary.

Continuation of the fight.

Whilst you are fighting the outbreak, you should change a minimum of 10% of the water every week, siphoning out as much detritus & algae as possible. Remember to keep cleaning the mechanical filter media as soon as it becomes soiled. This is an indicator of the success you are having in the tank. Check and change the Polyfilter as soon as it becomes used up.

At this time the algae bloom should be under control. However, it is still important that your carry out the maintenance to prevent the algae from returning.


Most recent revision: January 24, 2004

Copyright 2004
Richard Webber &
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