Following up on observations of changing fish behaviour when either lighting or flow rates are changed, here we take a look at what happens when the lights turn off.

The video shown starts after the Kessil A80 light has been on for nearly 6 hours, the typical photoperiod for the current setup.  The tetras and barbs are towards the bottom right portion of the tank, as they have been for almost the whole day.  Once the lights turn off (automatically) they become more adventuresome, and expand their range to the upper reaches.  To see whether this was a temporary reaction to the change in lighting the video also skips ahead to 30′ after the lights have turned off, and the fish are behaving in about the same way, suggesting is it the state of the lighting rather than the change in lighting that is driving their behaviour.

More thoughts after the break…

Lights turn off at 0:30
30 minute time jump to low flow at 1:25
High speed flow at 1:57

Continue reading “Fish behaviour: water flow vs. lighting – pt 2” →

In transitioning from a low tech to high tech tank I noticed a significant change in the behaviour of the fish* where they used to swim mostly at the top/middle regions of the tank under low tech conditions but then spent a lot of time at the bottom with the high tech conditions.  At the time I attributed this change in behaviour to the increased water flow from installation of a powerhead, but now I’m not so sure.

Embedded is a video that starts with the tank in a lights off, low flow state.  This is 4 hours after the lights have turned off for the day at which time the fish also got fed so they’re not behaving in a hungry mode anymore here.  After the first minute the powerhead will automatically change from low flow mode to higher flow, and after the 2 minute mark I’m going to manually turn on the main tank light.

Observations below…

 * The otocinclus catfish and shrimp don’t seem to care about either flow or lighting – they pretty much always behave the same way regardless.

High speed flow starts at 1:02
Lights come on at 2:20

Continue reading “Fish behaviour: water flow vs. lighting” →

I’ve been running the Kessil A80 light for 6 hours per day on the maximum intensity.  The aquarium looks nice either with the lights on or lights off so here are some contrasting photos.

With the lights on, the fish tend to stay at the bottom of the tank.  With the lights off they are considerably more adventuresome and happily explore the upper reaches.  They have also come to expect that shortly after the light turns off in the evening that it will soon be feeding time and eagerly start congregating at the top (and following me around) in anticipation but in this “lights off” photo they have already been fed.

I also recently changed the flow pattern by moving the powerhead so the flow goes across the width of the tank from right to left rather than from the back to the front so the ludwigia isn’t drawn in, and put the powerhead back down to a lower level which reduces the amount of shimmer considerably.  The fish always take a little while to adjust to a new flow pattern but it doesn’t take them long to figure it out.  With less disruption of the water surface in an open-top tank you might expect increased levels of CO2 retained in the water column, but with this closed lid aquarium there doesn’t seem to have been any noticeable effect.