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i've had a 10G marine tank set up since last january. it's stocked with a carpenter's flasher wrasse, a firefish, and a few snails and hermit crabs. they've all been in the tank for several months.

i do weekly water changes of about 25-30% and regularly check my water for pH, salinity, nitrite, nitrate and ammonia. everything checks out ok.

anyhow, recently there has been a reddish-brown algae growing on the substrate (which is aragonite). i gravel vaccuumed it last week, and it has come back very quickly.

just curious as to what's causing this... i'm thinking that my mom possibly overfed the tank while i was away for the weekend, but i'm not sure.

let me know! thanks in advance

Have you checked your phosphate levels?

Elevated phosphate levels will also trigger an algal bloom.

Two things you need to do. One, check your tap water and see if that is inputting phosphates into your system at source. Of course, if you've bought an RO unit and you're using that, then you'll eliminate phosphates from the tap at source. If you're using tap water without an RO unit, then that could be adding phosphates to your aquarium 'behind your back' so to speak.

If your tap water is OK, or you're using RO water, then your phosphate source is being introduced into theaquarium by other means. And yes, overfeeding is a superb way of whacking up phosphate levels to the point where an algal bloom launches a campaign for world domination, beginning with your aquarium.

Of course, the trouble is, your aquarium NEEDS an input of some phosphate, for several reasons. One, beneficial algae (the green variety that fishes such as Centropyge Dwarf Angels graze upon) needs phosphates, and two, your fishes need phosphates to help build their skeletons. Calcium phosphate is a significant contributor to the mass of bone. Third, the molecule that governs the release of energy in animal muscle is - wait for it - adenosine triphosphate. So you need phosphates for your fishes' muscles to function! Finally, phosphates play a big role in the structural integrity of DNA - and this applies to everything from single celled cyanobacteria to humans. So, as you can see, phosphates have a major role to play in life!

The trick here of course is to balance everything. And, it's possible that while you've been careful yourself, your feedings have just slightly contributed to a net gain of phosphates overall in the aquarium, and they've built up over time. A 'stealth' growth of phosphates like this can be difficult to control if you're not aware of the issue. Then, of course, it only takes one accident (such as your mother overfeeding during the weekend) to push the levels to the dizzy heights of eutrophication, and wham, nuisance algae drop in and thank you kindly for the feast.

Trouble is, controlling the input of phosphates is not easy. As I said, you need to input phosphates in the food you give to your fishes to help them maintain skeletal integrity (as well as those other critical biochemical roles I mentioned). Trouble is, quite a few prepared foods (including specialist marine foods) contain elevated levels of phosphates. Which your fishes duly excrete.

Now, controlling phosphates (which is VITAL if ever you move onto coral cultivation by the way, at least according to DAvid Saxby, whose monster reef aquarium was featured in Practical Fishkeeping magazine a while back) is a somewhat taxing exercise even in a large aquarium. David Saxby has FOUR THOUSAND GALLONS OF SEAWATER to dilute his phosphates with, and he gets through 50 kilos of RowaPhos a month in an effort to control them! But then his aquarium is on an industrial scale, and a LONG way removed from your nano system

The reason I've highlighted that monster aquarium is this. If it's hard enough for David Saxby to control phosphate levels with 4,000 gallons, you're REALLY going to have your work cut out controlling them in 10!

If you can do it, the measure I'd adopt is this - make your nano system part of a coupled pair, with the other being a refugium in which you cultivate something that will mop up the phosphates (and for that matter nitrates as well). Nature supplies quite a few handy nitrate and phosphate "hoovers" for the purpose, in the form of algae. The important point here being that in the refugium, you cultivate an algal species that you choose to cultivate because [1] it makes your management of nitrates and phosphates easier, and [2] the species you choose is easier to handle than the 'nuisance algae'.

So, you could run with macroalgae - a refugium full of lots of Caulerpa for example - or you could cultivate filamentous green algae on plastic lattices slotted vertically in the refugium. Either way, you have a means of removing the excess nitrates and phosphates via a simple two stage process - your cultivated algae absorb them into their own tissues, and later on, you harvest the algae. The surplus can either be tossed into the bin, or, if you have a fish in your aquarium that eats the stuff, you've solved part of your fish feeding problem at a stroke, and you're saving money into the bargain by growing your own fish food.

Remember, if there's a water management problem to be solved, chances are Nature has already provided a solution. After all, Nature's had three billion years to work on the problem, and thus has expended rather more in the way of R&D effort on the project than you'll ever be able to manage. So, track down the solutions Nature has provided, put them to use, and chances are that will solve the problem of the moment with much greater ease than trying a 'technological fix'. Likewise, if there's a pest critter loose in your aquarium, the best solution usually takes the form of something that regards your pest critter as lunch - there are few more powerful motivators toward pest control efficiency than hunger on the part of the pest controller.


Panda Catfish fan and keeper/breeder since Christmas 2002

wow- what an answer! thanks so much : )