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.

Now that the plant is settled in and well-established (19-Dec-2020) it’s at 17 cm and while the tops are still attractive, it has an exposed bare understory layer with plentiful “aerial” roots – at least that’s what they’d be called if the plant weren’t underwater – that are somewhat unsightly.  I’m not sure what to do now, so I’ll take some advice from the UK Aquatic Plant Society.  Some possibilities are to plant something smaller in front to hide the bare stemmy rooty patches which would need something small that doesn’t mind being shaded, or alternatively there might be a trimming method for the lobelia that would keep it small(er) and filled in on the bottom, as it was a couple months after it was planted.  Alternatively I suppose it could be removed and replaced with something else, but I like the pretty bright green appearance of the leaves and it is thriving in the tank.  I could take the front ones out I suppose and leave one or two in the back which would then give some light for something else in front.

It’s challenging with a small tank getting the CO2 flow to be both low and stable.  I use 600g disposable CO2 cylinders with a single stage regulator that is ok, but not very useful for fine control.  There are several downstream valves that further reduce the gas flow.  The CO2 over the last month or so has been fine, but yesterday and a few days before the flow has been creeping upwards as measured by the bubble counter and today was coming through more than what I’d like, with the drop checker appearing the morning after a 50% water change a little aggressively pale in what might be the 35 ppm CO2 range – that’s ok for today but could be problematic at this rate over the next few days.  I adjusted the CO2 at the regulator down from 10 L/min to 8 L/min – going much lower than this is quite unreliable – then tweaked the downstream controls to get back to 120 bubbles / min which is about right.  Something to keep an eye on over the next few days.

The Kessil LED light and LED lights that come as “point sources” rather than as strips of lights can have a feature called “shimmer” which is where they make ripples of light on the bottom of the tank.  I’ve never really observed that with my set-up in the past, attributing that to not having the light over open water but rather shining through a clear lid that gets condensation on it for a more diffuse type of lighting.  Recently however I had to relocate the powerhead up higher in the tank to avoid getting the ludwigia sucked into it and that resulted in a lot more surface water turbulence.  Suddenly, there’s all kinds of shimmer-like effects.  Is that was people generally mean – that the effect is caused by wavelets on the surface of the water?  The powerhead alternates every two minutes beween the lowest setting, and the next-to-lowest setting, and while on the lowest setting the shimmer is visible – look on the sculpture inside the tank and on the roof of the fireplace above the tank – on the higher setting it is very apparent.  Some people like shimmer and some don’t; I didn’t even notice it until a week after adjusting the height of the powerhead.  When the powerhead is deeper in the tank there is still a lot of water flow but the surface stays relatively calm and there’s no “shimmer”.

The fish don’t seem to particularly notice or care in either case.

Videos included after the break…