Should I switch my sump to live rock?

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One PFK reader would like some advice on whether she can switch her sump to live rock. David Wolfenden offers his advice...

Image: Neil Hepworth.

Q) My marine tank has been set up for 14 years and contains fish and soft corals. Filtration is a sump with three compartments, one of which holds Caulerpa and a sand bed which requires a constant LED light for maintaining growth. There is also a protein skimmer running constantly. There is good growth on the corals and I carry out a water change every two weeks.

If I decided to change to a coral and clean-up crew only tank, could I switch my sump to live rock, taking out the sand and Caulerpa, thus enabling me to switch off the light and the protein skimmer in the sump?

CAROL LAST, VIA EMAIL

A) DAVE WOLFENDEN ADVISES: From the sound of it, the system seems to be working really well as it stands. If you’re pleased with the coral growth and not having any problems with the overall health of the inhabitants, I would suggest keeping the sump as it is.

The set-up sounds ideal. In fact, the Caulerpa will be assimilating nutrients as it grows, and as you harvest it, nitrates and phosphates will be exported; the skimmer will be helping to export organics; and the sand bed on which the Caulerpa sits is no doubt teeming with macro-and microorganisms which will be processing and cycling nutrients.

If you were to eliminate the fish from the system, then you’ll certainly reduce the nutrient input due to less feeding, but either way I think getting rid of the skimmer is a pretty drastic move, and having one would still be very beneficial in maintaining low nutrient levels, regardless of whether fish are present or not.

Similarly, if the macroalgae is doing the job, you run the risk of putting the system out of whack if it’s removed, although removing this and replacing it with live rock would be less drastic than removing the skimmer. Ultimately, it’s your call, but if this tank has been running successfully as it is for a number of years, I don’t see any benefit in changing the sump’s components.

How does it spread?

Caulerpa spreads by sending out runners but it can also reproduce sexually. This second method can cause problems in the aquarium, as after reproducing it dies back, quickly becoming a mushy mess with an associated pollution risk. Caulerpa kept under 24-hour lighting is less likely to sexually reproduce and regular pruning may also reduce the likelihood of sexual reproduction occurring.

Watch out for the appearance of small, stalked reproductive structures known as gametangia on the blades and remove any Caulerpa from the aquarium that shows signs of these forming.