full height ludwigia and lobelia
Ludwigia breaks the surface

How tall do submerged aquarium plants grow?

Figures are approximate, as they say.  When planning a planted aquarium (and there should be some type of plan!) it’s important to consider the expected maximum height of plants in the layout.  I went wrong previously planting echinodorus radicans, a fine plant but much too large for this aquarium.

After not trimming back the ludwigia last week today it managed to reach the surface of the water.  This version of ludwigia, ludwigia mini ‘super red’ is listed online as “Dimensions: grows up to 30cm” however in this aquarium it is 41 cm from the aquasoil floor to the water surface, so this plant has overachieved.

I can’t complain and I’m glad it’s healthy.  I’ll give it a trim today and replant some of the better looking top portions to have it fill in a little to the right.  Stem plants like the ludwigia are pretty flexible that way:  you can trim them to pretty much whichever height works for you, just the growth rate and how much you trim will determine how often they will need this type of maintenance.

Afternote: 
Digging around a bit more on the Tropica entry for this plant it says in the “Plant info” section in the ‘Height’ entry if you click on the +/- expander button:

Height: 10 – 30+
Average height (cm) of the plant after two months in the tank.

so to be fair there is a little + sign after the 30 and it does say ‘after two months’ and it has been three months in tank (nearly to the day) since it was planted, so I suppose it’s “fair play” to the description, even if 30+ is actually 41…

Ludwigia palustris mini ‘Super Red’ can go back to green at the water surface

Just to see what would happen, another time I let the ‘Super Red’ go for much longer than I otherwise would have and it reached the top of the water and kept growing.  It kind of piled up on the surface without reaching directly through and I noticed that the new growth at the surface had green foliage rather than red.  When first planted back in the day the emersed form of the young Ludwigia was also green rather than red, and it seems the red colouration may be exclusive to the submerged form.  The pile of Ludwigia floating on the surface was shading everything underneath so I did eventually take it all out and replant the tops.  Ludwigia tolerates this procedure really well and I have successfully done this a number of times now without adverse findings.  Some of the ‘mini’ stems had comfortably exceeded 50 cm in length, so the ’30+’ guidance from Tropica could fairly be listed as 40+, or maybe 30+++.  Once back to being fully submerged, the new leaves produced subsequently were back to the usual bright red colouration.

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

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

Fireplace Aquarium with lights off
5-Jan-2021 Lights off
Fireplace Aquarium with lights on
5-Jan-2021 Lights on

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.

Ludwigia palustris post-trim, aquarium with lights off
Post-trim aquarium – lights off

Today I gave the ludwigia palustris its first trim. A couple of the stems were just under the surface so I clipped off the three tallest.  This ludwigia, in contrast to some reports, doesn’t have very many aerial roots but where there were a few part-way down the stem, I trimmed to just above the node below the roots to allow (hopefully) new growth, then clipped off the stem to just below the node where the roots are and planted those pieces on the far left of the tank in a region that was more thinly grown, very likely due to less light off to the side and in the shade of the taller stems in the centre.

Ludwigia palustris trimmed tops replanted
Ludwigia tops planted behind the lobelia cardinalis ‘wavy’

I was following this guide to trimming stem plants from dw1305 so we’ll see how that goes.  Seems straightforward and reasonable.  There was some question as to whether the shrimp would just immediately dig up the newly planted tops, but happily that hasn’t happened yet.

Lobelia cardinalis 'wavy' nearly full-grown submerged
19-Dec-2020

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.

Drop checker mid-light green colour
Drop checker – the photo makes it look a little darker than it it appears by eye

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…