Problem solved?
I am hopeful that I may have found the solution to my restless and panicky chilli rasboras. I've made three changes during the last week, and I think the combination of these changes might have worked.
The first change was to swap the lily pipe for a spray bar. The spray bar is a little too long and needs shortening, so it's at a diagonal across the back of the tank for now, with the the holes pointing upwards towards the surface and somewhat backwards against the glass to reduce the force of the flow. I also need some elbow connectors so I can put it at a more horizontal angle, probably near the bottom of the tank pointing upwards. Hoping to make these adjustments today during a water change. The chillies do seem to prefer the more diffused water flow.
I will need to experiment with the direction of flow to get decent CO2 distribution. My drop checker now goes blue in the mornings whereas with the lily pipe it previously stayed green, even when the CO2 had been off for many hours. This possibly indicates better surface gas exchange with the spray bar; I do think I've got a bit more surface turnover now despite the more gentle flow overall, which is no bad thing. I may also consider having a CO2 'on' period during lights-off simply to prevent the CO2 level going too low. The challenge will be to make sure that my foreground carpets of HC and Glossostigma get enough CO2 without creating strong currents that upset the chillies.
The second change seems to have had a significant effect: more chillies. Lots and lots more chillies! I went back up to Sweet Knowle Aquatics near Stratford Upon Avon a few days ago, which is the only shop I can find that has them in stock at the moment. Fortunately it's also a truly excellent shop for freshwater tropical fish - the quality of fish is quite the best I have come across in several decades of visiting fish shops. Well worth visiting!
I decided to get another dozen chillies to add to the six already in the tank. I know that's a huge increase, but I'm confident the tank can take the extra bioload - it is quite heavily planted and has a canister filter full of ceramic balls with a rough surface for bacteria. I will monitor ammonia carefully as the tank adjusts, and add an occasional dose of Prime as a precaution.
On the day after adding the newcomers the chillies did look quite a bit more chilled. They have dispersed a bit more, and are not constantly chasing up and down the sides of the tank or hiding in a corner.
Aesthetically it's not quite what I was aiming for with the tank: I originally wanted just a very small number of tiny fish to set off the planting and give my nano tank an illusion of scale, but I'd far rather have a larger number of relaxed fish rather than a small number of panicky fish. I have removed my ridiculous rubber fish! I don't think the real chillies were impressed by them anyway.
The third change I believe has made things better still for the chillies' stress level. I have installed an LED controller, which ramps the lights on and off over a configurable period of time as well as allowing me to limit the maximum brightness if I need to. With this, it seems I can ramp the lights up over a few hours all the way to full brightness and the chillies don't seem to care.
I didn't realise that the controller I ordered only allows a single photo period per channel, so I bought some 5.5x2.1mm DC plugs and sockets from Maplin and made a connector that links two plugs and two sockets together. There was much swearing yesterday because my soldering skillz are so poor, but I got there in the end! I can now plug both lights into both channels 1 and 2 of the LED controller, effectively giving two photo periods for both lights together instead of controlling the lights independently. I will find it useful to have a short lighting period in the morning (which I have configured much dimmer than the main period) so that I can feed the fish when I get up. I have configured the main photo period to ramp the lights up over a 4 hour period and then immediately back down over 4 hours; I can reduce the ramp period to 2 hours if all goes well. The controller has a third channel, which I'm not currently using.
Oh, and there is one other 'change' that has been happening over the last week or so: I've been allowing the hornwort to grow unchecked, and it's now formed quite a thicket of floating strands at the surface which is beginning to fill the tank top-down. I will prune and replant some of it so that it's not choking the aesthetic picture of the tank, but keep some of the surface cover in case that's part of what's making the chillies more relaxed.
At last, the chillies are doing what chillies should do: they strut around the middle of the tank like minuscule aquatic chickens, rather than charging around like mental cases. They're not schooling as tightly as they were, which although it was aesthetically pleasing it did indicate an element of stress. Some of them are beginning to colour up a bit as well.
Happy days, I hope!
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