About 6 weeks after fish were added to my new tank, the water turned green. It's in a room that gets a huge amount of natural light, the tank even gets a few minutes of direct sunlight each day, and that's not going to change. It's an African cichlid tank with a high pH, and I'm not sure plants are going to be a workable option, though I plan to try it some time in the future after I have a hood and lights installed. I read varying reports on the internet about whether a UV sterilizer can cope with this problem: the argument against is that given adequate nutrients and sunlight, algae will find a way to grow; the only real solution is to remove the nutrients (e.g. by growing other plants). Two weeks after installing a Turbo Twist "Pond" (yeah, right) sterilizer, the problem has been reduced to an unobtrusive but still detectable level. The shots below are taken from the side, looking down the 7 foot length of the tank. It's only 16 inches deep, so from the front the water's now quite clear. The water was most green 1 day after installation because the color was varying more strongly then day to day, depending on weather and light.
 |
| Day 1 |
 |
| Day 2 |
 |
| Day 3 |
 |
| Day 5 |
 |
| Day 9 |
 |
| Day 14 |
Details: Tank is about 135 gallons, with 2 Eheim 3e 2078 canister filters each rated at 400+gal/hour flow. Each filter has an inline heater in the outflow line. I added a Turbo Twist 6X to one of the outflow lines which visibly reduced its flow, compared to the other, so maybe it's in the 250-300 gal/hour range now. There is still algae growing on the rocks and gravel, which is kept under control with algae eating fish.
Update: 2013/01/03
The Coralife TurboTwist UV sterilizer failed after about 6 months. It was troublesome from the start: the plastic parts are brittle and easily broken, which was the final failure mode, but the bulb also failed to seat well in its socket making its performance flakey. I don't recommend this unit as it proved to be low quality and non-robust.
For the time being I'm doing without a UV sterilizer, though I may try another model in the future. I've added plants to the tank and increased the light greatly. I'm going through various algae blooms again, however not green water this time. I've read elsewhere on the web that green water will burn itself out and clear after a few weeks with consistent tank care and no UV sterilizer. I don't have much evidence one way or the other, but it's possible that my positive experience with UV sterilization was at least partly fortuitous timing with a natural cycle.
Update: 2014/01/20
Adding plants to an aquarium makes the algae control problem much more complex, because one needs to maintain some level of nutrients in the water. Last spring I decided to add another UV sterilizer, due to very bad outbreaks of BGA (cyanobacteria). It didn't seem to help much with that problem, but I"ve kept it running on the suspicion that maybe it helps slow some algae and pathogen outbreaks, more than it may interfere with some beneficial processes. Who knows. In any case, this time I installed an Aqua brand UV sterilizer which I can recommend as a well designed and constructed unit. Mine has been trouble-free for close to a year.
