Algae: the good, the bad, the ugly
Say the word "algae" anywhere within earshot of one or more aquarists and you are undoubtedly going to hear less than kind words about it. It is possible you're hear the sentiment that all algae on the planet should simply die, and preferably a painful death, because of the frustration it causes aquarists. Imagine a world without algae: that's not hard to do, think of the moon or some other lifeless chuck of rock in space, for without algae, life as we know it on earth would cease to exist. Algae, in the form of individual cells and colonies moving freely in the oceans - pelagic phytoplankton - accounts for the generation of much of the oxygen produced on this planet, to say nothing of the food it serves as for a myriad of animals or the symbiotic relationships it exists in with things such as corals, anemones, lichens, so on and so forth.
Why is algae like it is, and not a tree bush or shrub? It's a very very primitive plant and comprises the bulk of what we call "non vascular" plants, that is, it has no veins. All algae are non-vascular plants, but not all non-vascular plants are algae - although it's close. The liverworts, Riccia being the most commonly known liverwort, are also non-vascular; every other plant in the aquarium besides Riccia and algae are vascular. This gets a little fuzzy though in the strictest sense, as certain brown marine algae do indeed have some semblance of a vascular system. So what exactly are algae anyway? Biologically, the name "algae" is given to a group of organisms of mixed affinity. The word itself has no taxonomic significance whatsoever. One way to define what the algae are is to assert they have lack any organization of their reproductive systems, but certain red algae have reproductive structures; they're a diverse bunch! To give you some idea of the diversity, not all algae are even plants - the blue green algae have been moved out of the plant kingdom into their own taxonimical niche. In the two kingdom model, now deprecated, there was an animal and plant kingdom. More modern is the five kingdom model: animals, plants, protists, fungi and kingdom monera. The algae are contained in three of these kingdoms: Protista (Eukaryotic algae), Monera (Prokaryotic "blue green" algae) while the rest fall into the plant kingdom. Genetically, the blue green algae resembles bacteria more than the familiar green algae, but this does not mean they are bacteria, just that they resemble them more than they resemble any other species. No wonder they have their own kingdom.
"algae" is the plural term; "alga" is the singular, "algal" is the adjective form: "In my tank I have so many algae it's just not funny, the one that I really like is the alga Cladophora aegagropila, and if you want some I could send you a few algal cells".
The algae are polyphyletic, that is there are many lines of evolution that lead up to what we consider today to the "the algae". It has been suggested the red algae belong in their own kingdom as well. No other form of life on this planet has this kind of diversity.
No other form of life on this planet has the distribution or hardiness of the algae. They exist in every major body of water on the planet. In lakes, rivers, streams, waterfalls. In fresh water, in salt water. In hot springs. In the arctic and antarctic. On snow - in some parts of the world red snow algae colors snow beds. In the desert - in some parts of the Namib desert in Namibia algae grows underneath quartz rocks. Light passes through the translucent stone and enough moisture is trapped under the rock that the algae can actually grow.
Perhaps the oddest place you'll find algal growth is the fuel tank of your car - if you have a diesel that is. In warm climate, diesel drivers can be all too familiar with the blackish algal deposits that can clog filters and strainers and render an otherwise perfect can into a paperweight until the algae is removed. In warm climates, diesel owners routinely use (or should use) an algicide to prevent this. The algae does not live in the diesel fuel, it lives in water deposits in the tank and the diesel fuel does not seem bother it. So don't get frustrated if you have a hard time killing algae in your tank, even diesel fuel doesn't bother this stuff. This is one tough organism.
Enough science class, back to the good, the bad and the ugly. First the good: Cladophora aegagropila or "algae balls". Cladophora is a very diverse genus, with species ranging from marine kelp, slimly stuff that grows on rocks on the seashore, thread algae in ponds (ugly, more on this later) and this decorative species - arguably the only decorative freshwater algae. Certainly the only one you can actually sell. It's very slow growing but also very decorative, and a bit of an oddball (no pun intended) in the aquatic plant world. You won't see it often, but it is available from specialty plant suppliers and you do see mention of it from time to time on the net. Made popular in Japan and cultivated primarily in Denmark, it's reasonably well established in North America now, although it's slow growing habit and odd appearance means it's probably not ever going to be as common as Vallisneria or Sagitaria in in the pet trade. It has a couple of annoying drawbacks - it's fine filaments tend to collect mulm, but this is easily fixed by taking it out of the tank, rinsing it like a sponge in some clean water then putting it back in the tank. Sometimes the ball will develop air inside and it tends to float, like some green hairy mine. The solution here is to weigh it down or attach it to something with some fishing line. It won't normally attach itself to anything, but, if the ammonia levels spike it will reproduce by spores and what looks at first glance like a thread algae infestation is actually new colonies of C. aegagropila attaching itself to various places in your tank.
While not decorative, there are other useful algae routinely found in aquaria. The only thing I've every been able to successfully feed to Daphnia is algae in the form of "green water" - suspended algal cells. Some people claim yeast will work, but no matter how little I use I always found it to make an awful fuzzy mess that kills more daphnia than it feeds. But green water - that's another story. And it's dead easy to grow by just sticking a bright light over a well aerated tank and scraping some green algae from somewhere and stirring it into the water. Absent strong filtration, the tank should go green in no time and the water can be fed to very small fry or to daphnia, or daphnia can just be thrown into this tank; they'll clear it up in about a week. When this happens you'll either need to have more food ready for the Daphnia or plan on feeding all this daphnia to your fish fairly quickly.
The bad: almost everybody has algae in their tanks. If you don't, your water is not capable of supporting plant life and chances are high something is amiss. Usually it's not a problem: if water is changed regularly so wastes don't build up, and it plants are well fertilized to out-compete algal growth you really shouldn't have much of an issue with algae in your tank, and you may just have the odd spot of green. This is easily scraped off with a razor blade right before you change the water. Of course you turned the filter off so it'll settle on the substrate where it can be easily siphoned up.
The other common problem in aquaria with algae is cloudy water. Often mistaken for a bacterial bloom, suspended algae is the most frequent cause of cloudy water. Turning the light off for a couple of days and not feeding usually makes it go away. The easy way to tell if cloudy water is algae or really a bacterial bloom is to put a diatom filter on the tank. In about fifteen minutes, assuming the filter is in a good state of repair and working properly, the tank should be crystal clear and whatever was making the water cloudy will now be a residue on the white diatomacous earth on the filter bag. Chances are very high that the deposit you'll see will be green or perhaps yellowy green. That's algae.
The ugly: Thread or hair algae. Black brush algae ("BBA"). Red spot algae. These ones are heartbreakers. Left unchecked, the first two can completely fill a tank, choking out all plant life completely. The red spot algae is just plain ugly and virtually impossible to remove even with a razor blade.
Some people claim to be able to keep them under control with proper fertilization while others swear by rosy barbs, florida flag fish, various algae eating shrimp and Siamese algae eaters. Bully for them I say, but these have never worked for me and even if they did I'm not really interested in controlling them, I want them dead, eradicated, gone, fini, pushing up daisies. And there's only one way to do that. Algicide won't work, it's ineffective against this stuff.
You can get infected by these nasty beasts by feeding live food from a pond or by receiving plants from somebody who has the stuff. Even if the plants you get look ok it only takes one lousy cell to infest your tank.
The cure for this is not pretty, it does not smell nice and it's a lot of work. But it does do the trick, and once you've eradicated the stuff you'll want to quarantine everything coming in to prevent re-infestation, and I mean everything. One cell, just one lousy cell and you've got a problem again.
The cure: bleach. No kidding. Household bleach. Increadable as it may seem, your delicate looking aquatic plants can actually withstand being bleached, although they will lose likely drop some or all of their leaves - especially the more tender plants such as Crypts - but they will regenerate. I've never seen bleach kill a plant outright.
You'll need one part household bleach to nineteen parts water. Place this in a bucket, immerse the plants in it fully, then rinse the plants thoroughly in fresh water. Adding some chlorine remover wouldn't be a bad idea although I never bothered with it. Most plants can take about 2.5 minutes of this. The tougher the plant the longer it can take. The aquatic ferns and mosses seem to suffer the worst, tough plants like Anubias you'd swear can grow in the stuff. Algae may nto be bothered by diesel fuel, but bleach turns it white almost instantly.
Sounds horrendous, I know, but once you've done it it doesn't seem that bad. Of course this is just the beginning. Remember you have to kill every cell of the wretched stuff so the tank itself must be bleached, and this is probably better done if it's completely drained; rather than 2 minutes with a dilute solution of bleach you're probably better off wiping it down with full strength bleach. Note that you will want to wear rubber gloves and goggles to protect your eyes while you're doing all this. The gravel or whatever you use as substrate must be bleached. Filters, nets, ornaments, heaters must be bleached. Did you ever touch your doorknob with hands wet from a tank infested with thread algae? Bleach it. Remember: one cell is all it takes. Bleach everything.
Obviously you can't bleach your fish - well, ok, you can but they won't survive - but they will have filaments of thread algae in their gills and in their gut. The thing to do with them is put them in another (sterilized) tank with little or no water movement and fairly course gravel. The algal cells will fall into the gravel - 3 days of this and they'll be safe to introduce into your now algae free tank.
Snails are the hardest to deal with. They'll actually survive bleach in many cases because they'll close up their shell and keep the bleach out. Of course they'll holding algal filament laden water up inside their shell and will re-infect your tank as soon as they're put back in. So, your options here are to obtain new snails that are unquestionably algae free or to put them in a small tank with some course gravel and black it out and leave them there for about 3 months. You'll never be able to purge your snails of algae but their offspring will be ok. You can feed them one piece of dry cat-food once a week or so. If you have Malaysian live bearing snails in your tank you probably will need to just get new gravel. You'll never get all those snails out and each one will have thread algae filaments in them. It's probably best to clean your snails 3 months before you tear down and bleach your tank so you have clean snails for it when it's ready.
Yes, it's a lot of work. But it really is the only way to eradicate, not just control, the most ugly forms of algae.