How do I control this grass-like algae?


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Dave Wolfenden offers advice for a reader who's having a turf war in his reef tank.

Q. I was wondering you might be able to offer some help with controlling an algae outbreak in my aquarium. The algae seems to grow from the coraline algae and is a very dark green, wiry and hard grass-like algae. It requires a bit of force to remove it.

My parameters are: NH3 nil, N02 nil, N03 <5ppm, Phosphate nil, pH 8, KH 10°, calcium 420ppm, sg. 1.026, temperature 25°C/77°F — done using API tests except pH (Salifert).

Lighting is TMC AquaBeams with white and blue LEDS mixed on each strip, controlled at 70-75% with the TMC controller. Lights are on fade from 10am till 12noon, on fully til 6pm and fade off by 8pm.

For filtration I'm running two powerheads, V2 400 skimmer, Fluval 306 with just Rowaphos and Purigen which is replaced monthly. The tank is 125 l/27 gal and has 25% water changes weekly.

Stock is a False clown, Yellow goby, Sixline wrasse, Coral beauty, two Yellow-tailed blue damsels and a Red Scooter Blenny, along with a green Bubble anemone, a Knobbly toadstool coral, Jasmine coral, plus colonies of Zoanthus and Blue mushrooms, two feather dusters, hermits, Turbos and a Cleaner shrimp. There’s 12kg of live rock in the tank.

The issue probably began way over a year ago when I was running standard fluorescent bulbs. But now I'm considering a larger upgrade so I would like to figure a way of controlling it or beating it if possible. Can you help?

Andy, email

A. From your description, I’d suggest that this might be a species of Cladophora, which also answers to the name of 'brush alga'. It’s quite tough stuff, and as you’ve discovered it’s pretty resilient too. It commonly ‘hitch hikes’ on live rock, and can appear many months after the rock is introduced. There are two approaches to controlling algae — limiting nutrient input and removal — either manually or through biological agents.

Manual removal can help to an extent, but the algae will simply grow back. Not many herbivores touch these wiry algae, and your choice is limited anyway due to the size of your system and its existing inhabitants. A tang isn’t an option as even a small specimen needs much more room. An Emerald crab (Mithraculus sculptus) might eat it, but these can be quite aggressive and cause their own problems.

On balance, I’d suggest that you concentrate on limiting nutrients, specifically nitrate and phosphate, to put the squeeze on this unwanted visitor. Although your readings for both phosphate and nitrate look fine, here’s the thing: there may be unacceptable amounts of these algal fertilisers being generated in the system, but the algae is actually assimilating them, meaning they are not being detected by your test kit.

Review feed input to the system, and make sure that excess food is not being added. Washing frozen feeds to get rid of residue can be useful to limit nutrient input. Ensure that the skimmer is functioning optimally, and give the tank’s substrate a really good clean on a regular basis.

Although you’re already performing 25% water changes weekly, I’d suggest increasing the frequency of these to twice a week, and if you’re not already using RO water, then seriously consider it.

It might be worth thinking about upping the tank’s mechanical filtration, and — if it’s not the case already — part of your external filter could incorporate a mechanical sponge, which should be frequently rinsed in tap water to prevent build up of detritus, and to stop the media from becoming a biological filter (which may contribute to high nitrate levels).

Algal issues arise due to an excess of nutrients, and by reducing the input of these (and ensuring their swift removal from the system) it is possible to curb the problem — in time...

Dave Wolfenden

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