boomer wrote: ↑Sat Jan 08, 2022 12:17 am
It's better to have the tank light period consistent, rather than breaking it up. Since you're not home from 5:30 am to 6 pm, it makes sense to have the light on when you're there to enjoy the aquarium. You can set the timer to turn the light on during the day, say 12 noon or 1:00 pm, and off at 8 pm or 9 pm, depending on your schedule.
There are a couple of things to consider. Firstly, the room shouldn't be in darkness when the tank lighting comes on or goes off. You want ambient room light, whether from a window during the day or artificial lighting at night, for at least half an hour before the tank lighting comes on and after it goes off. This helps avoid shocking the fish with sudden light/darkness, which isn't natural. You're aiming to create a sort of dawn and dusk, like in nature.
Secondly, there needs to be a period of continuous complete darkness during each 24 hours. This is when the fish's biological processes slow down, and they relax. It's similar to our sleep. So, in the example above, this would be from 9 or 10 pm, after the tank lighting and all ambient room lighting is off, until dawn when daylight may enter via a window.
The reason for this has to do with the circadian rhythm, a biological clock that runs on a 24-hour period. Fish, like all animals, have this rhythm, which is governed by light. Not only do their eyes perceive light, but their cells do too. This is why we experience jet lag, and there are problems when daylight savings time occurs. In fish, this light/dark response is even greater; every cell on their body reacts to light and dark.
Once you establish a regular tank lighting schedule, you'll notice that the fish will come to expect the light coming on and going off. That's because of their circadian rhythm. Experiments with blind fish have proven that this response doesn't depend on the fish's eyesight, but because every cell is affected by light and dark.
This is why the tank lighting period should always be continuous and roughly the same every day. It makes the fish's life simpler, as they can save energy for more important things, and there's less stress when everything occurs the same day after day. Some high-tech planted tank aquarists might suggest the siesta approach, but biologically, this is harmful to the fish. Plants can adjust to varying periods, but fish can't, at least if we want them to be in the best health.
If algae is a problem, reducing the tank lighting period is the best way to deal with it. Sometimes, an excess of fertilizers can cause algae too. But it's better to sort out the light/nutrient balance rather than jumping into something that will be stressful to the fish.
