The Mystery of the Murky Water

The goldfish (Moesha and friends) have relocated to a spacious outdoor pond behind the pet store. The antibiotic treatment of my tank for fin and tail rot has run its course. Maude (the swordtail) and a little catfish had the tank to themselves when a new issue emerged: murky water.

I noticed slightly greenish water after the first of four rounds of antibiotics. I figured the white powder reacted with something and changed colors. As the green deepened over the course of the week-long treatment, I wasn’t concerned.

The green water got worse in the days following the treatment. Replacing about a third of the water several times lightened the green, but only temporarily. Within a day or two, the water turned greener than ever.

When faced with a problem, I did what I always do: a Google search. The problem turns out to be an algae bloom. Possible causes include too much light, too much food, and/or too much waste. Removing the goldfish solved the excess food and waste issues. The light may make things worse, but is necessary for the plants.

Bacteria break toxic ammonia (fish waste) into harmless byproducts. This “nitrogen cycle” is central to the health of the tank and its occupants. Changes, like adding a fish or two, mess with the nitrogen cycle.

The antibiotic killed all the bacteria, bringing the cycle to a screeching halt. Algae stepped in to fill the void. Once established, getting rid of a green algae bloom is practically impossible.


I scoured the internet for options. A dude on YouTube eliminated the problem over fourteen days with a UV light and frequent water changes. He got the light online for forty bucks.

A filter system with a UV light for the pond has been on my wish list for a long time. The few I looked at ages ago were more filter than I needed for more money than I wanted to spend. A quick search turned up a model similar to the one demonstrated in the video from Chewy. Mine arrived Thursday.

Hooking up the UV-sterilizer was easy enough. I didn’t expect two power cords–one for the recirculating pump and the other for the light. As water passes slowly through the tube, UV light kills algae, bacteria, and parasites.

As I write, the UV-sterilizer has been running for three full days. Granted, my vision leaves a lot to be desired, but I see no difference in daily pics.

Took 14 days for the YouTube dude to clear up his tank. We’ll see if mine takes as long. I’ll keep you posted.