By Bob Goemans
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Bob Goemans corresponds with Robert Mallinson

Robert Mallinson writes...

Hi Bob,

I'm needing some advice regarding the use of activated carbon, as I have just received delivery of an Aquamedic carbon reactor. The usage advice being given is confusing to say the least. The advice from two mail order companies is that I should run the reactor constantly changing the carbon every 4 weeks. Some others I have spoken to say change it every 7 days. Others are telling me to change it every two days. Then there is the owner of the local fish shop that say's not to use carbon at all, but to use SeaChem Purigen. You now can see my dilemma! What I would like to know is your thoughts as to how much, how long and how often?

I have a nine-month-old 68 gallon tank with 14K MH running for ten hours per day. I'm currently struggling to contain diatom and cyano problems, as the sand is constantly a brownish green colour. Diatoms are beginning to cover the live rock and cyano is constantly building up on my Koralia pump as well as covering some of the Caulerpa in my sump, which is lit 24/7.

I plan also in the next week to purchase another Koralia pump to further the circulation in my main tank. I am a bit concerned as one or two of my LPS stock does not seem to be looking at their best. I check my water on a weekly basis and all is well, with phosphate reading zero. However, I understand that some phosphate kits don't always give the best of readings. I do have a phosphate reactor running and have been using a brand phosphate remover called Ultiphos, yet am considering switching to ROWAphos as well as using ROWACarbon. Is carbon the best option and should I switch to these brands?

Since I've read a number of your responses it's probably worthwhile giving stocking and feeding levels. I have a pair of clownfish, leopard wrasse, juvenile Coral Beauty, juvenile Regal and Yellow Tang, and some snails and hermit crabs. I feed DT's Live Phyto Plankton daily and DT's oyster eggs once a week and also Cyclop-eeze once a week. I also harvest live copepods and rotifers every two weeks, which I add to the tank. In the morning I feed some Ocean Nutrition Marine Algae and in the evening a cube of frozen Gamma Feed alternating daily between brine shrimp and mysis. It may also be worthwhile mentioning that my nitrate reading is also Zero. I would very much appreciate you advice.


Robert Mallinson

Edinburgh, England

Bob replies...

Hi Robert,

Thanks for your email and lets address the activated carbon aspects first. I consider it one of the best chemical filtration substances on the market. In fact it should be considered a tool in our arsenal for helping maintain water quality. As to usage, placing it in a reactor or canister filter provides the best usage of the media, as all water must flow through it and agree it should be used constantly. Usage quantity depends upon the overall volume of water in the system, and its replacement on system bioload. I generally recommend one heaping tablespoon, which is about 8 grams, per 10 gallons for reef aquariums. Since I consider your system bioload quite high, usage timeframe needs to be reduced from the norm, e.g., 6 - 8 weeks, to no more than 4 weeks. Recommending weekly or less timeframes to change the media is wasteful in my opinion!

There are many excellent brands on the market, but selection should be based on aspects like appearance, size, shape, does it float and make a hissing sound while becoming wet, and is the package labeled phosphate free. As for appearance, a dull black indicates a fairly porous particle and should be preferred over a shiny black particle, which is less porous. The particle's surface should be slightly irregular or rather rough. The particle itself should be more round than flat-sided, which would block water flow and reduce adsorption sites. As to size, the most efficient is approximately the size of a pinhead or slightly larger. Some may think powdered carbon would be better than granular carbon, yet this is not so. A smaller particle size only increases its "outside" surface area and actually impedes internal water flow, an important aspect where 'activated' carbon is concerned. Much larger than optimum size produces non-uniform flow and retards effective/complete penetration.

As to SeaChem Purigen, that's an excellent product, however it does require bleach/several treatments to regenerate it. Whether that's' something you want to add to your maintenance chores, is up to you, but if so, I'm sure you'll be quite happy with it.

Moving on to diatoms and cyano problems, there are two situations here that need to be discussed separately, as activated carbon usage will not cure them. As to the diatom problem, that's probably caused by the amount of silica (which diatoms use to construct their walls) in the water used for evaporation makeup and/or water changes. You failed to mention where it comes from, but if using tap water, it should first be processed through a high quality RO and DI unit before being used for these purposes.

Furthermore, when cleaning brown algae from the aquarium side panels, don't just wipe the viewing surfaces clean by using back-and-forth motion with a cleaning pad. This only distributes the diatoms/silica back into the bulk water where it's used again to produce more diatoms on the surface just cleaned. Instead, place the cleaning pad at the bottom of the surface to be cleaned and slowly slide the pad to the water surface. Then quickly remove the pad and rinse in some clean water. Repeat as necessary. This way, the majority of the diatoms on the viewing surfaces will be "removed" from the aquarium. And if diatoms are building 'mats' on your live rock, siphon it out and replace with newly made seawater that has used processed freshwater.

There is one more annoying issue that involves brown diatoms and that is why they seem to come about after sand surfaces are cleaned/vacuumed. That happens because the colonization of nitrifying bacteria in the upper portions of the sandbed in the course of their biological processes produce small amounts of compounds containing silicates. In areas such as the bulk water and sandbed interface, these compounds with the help of light form diatoms, especially during the enhanced activity period associated with re-colonizing the disturbed area. On-going removal of heavily diatom-coated sand should be limited to only the upper most grains via a siphon tube.

Then there's cyanobacteria, always a good indicator of excessive nutrients in the bulk water and that the 'good' bacteria in your aquarium can no longer maintain a balanced environment. I think you need a new or different brand nitrate test kit, as I find it almost impossible to believe its 'zero.' As to what the animals are fed, I must say you have chosen excellent products! Nevertheless, there needs to be some thought given to the volume fed, and what percentage is actually eaten and/or goes to waste, as waste in the form of fish excrement and foods not eaten are at the bottom line cause of cyano! Therefore, I would begin there and reevaluate the products used and those that you see not fully being quickly consumed, reduced in volume being fed. I would also simply consider smaller volumes fed more frequently if possible. Keep in mind liquid-like foods dispersed into the aquarium water go mostly to waste. Therefore its necessary to specifically 'target' feed in controlled amounts when using this type foodstuff. And also being sure the recipient is ready to feed, so waste is held to a minimum, such as when feeding feather dusters/shrimp.

As to phosphate test kits, there are those that are somewhat more expensive, but worth their price when it comes to accuracy, as this compound is a must to properly control if one wants to minimize unwanted algae and cyanobacteria. My preference is the Merck test kit, which will render readings that will allow you to judge if phosphate levels are where they should be, e.g., <0.015mg/l. As to the media to use in your reactor, I am not familiar with Ultiphos, an iron based phosphate remover, which is the preferred form of media. I've used ROWAphos, Warner Marine, PhosBan, and several other brands in the past with very good success.

Possibly for better water movement in the aquarium, you may want to look at one of the SCWD models (, as there are now sizes up to one inch (2.5 cm) that can alternate water flows in the aquarium without adding another pump.

In closing, there are many quality water-purifying products on the market, and if used correctly, help immensely to maintain high quality seawater. But one has to equate their use to the input of nutrients into a fixed-size environment containing live animals that in turn need be sized for the systems overall volume. It's a 'balancing' act, one where desire of colorful species needs to tempered with what is needed to properly care for them. I think you can rectify the problems in your aquarium if nutrient input is curtailed, and that includes the use of processed water to alleviate the diatom problem, ...then better control the food being fed.

Hope this helps,



Activated Carbon

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