Advice Re Change Of Lighting

Hello,

Our x-ray tetras have 'transferred' their dislike of water changes to a dislike of the lighting, despite me putting on the room lights gradually beforehand and despite 'forewarning' them that I'm about to switch the light on so as it's not sudden. They dart and cower in/behind their cave and plants if the lights are on. It seems that a few days away from home, having left them in the tank with the lights off, has contributed to this dislike of their lighting. We have tried putting taller plants in to provide more coverage and putting plants on the surface to dim the lighting, and have tried to persevere with the lighting kept on, but it's clear that they don't like this and immediately revert to their normal, active selves as soon as the lights are switched off. They are now joined by some pygmy cories which I thought might help calm down their dislike/fear. Although we could leave them without a light, it would be nice to see them a little better - but without distressing them.

We currently have a Sun-Glo 15w bulb. Any recommendations for alternatives? Presumably it would have to be the same/lower wattage. I've seen marine/power/aqua/day-glo options. We don't plan to have live plants.

Thanks in advance for any advice/help.

Most small fish don't like bright lighting, in nature they don't like swimming around in the open where they would be easy prey for larger fish. They usually spend their time among plants or close in to the banks where there is cover from overhanging vegetation. To quote the profile here for X-ray tetras "The fish require areas of vegetation and do not like brightly lit areas so a dark substrate and some cover is appreciated".
You have said that you don't intend to have live plants but also that you have tried putting plants on the surface which is a bit confusing. I would always suggest putting in floating live plants for these small shoaling type of fish. But unless you have a densely planted tank, you are unlikely to ever see the natural behaviour and true colours of these fish. A darkish background on the rear glass of the tank might also help, if you haven't got one already. In my opinion, most people's tanks are far too bare for most small fish.

I know your tank is fairly typical of many, but I think from the perspective of small fish, it's really quite bare without much shelter to make them feel comfortable. If you are worried about going in for live plants, I would suggest  that you start by attaching Java fern to some of the objects in the tank, it may be all that you need.

I also wonder about the number and type of fish and if more of a similar type of fish would make the X rays more confident. I know you have tried this with the Pygmy cories, but they are a very different type of fish. I bought several used tanks a while ago and some of them came with a few small fish, mainly tetras. At first I put each type into a separate tank, planning to add more of each later. Under these circumstances, some of them were very shy and would hardly ever be visible, in fact in the case of Black neons and Black phantoms I really thought they must have died several times as they were impossible to find. After a while, I decided that more of these were not in my plans and so I put them all in one tank. Within a day or so, the behaviour of all of them changed, they all became much bolder and shoal together, never hiding away. The Black neons went from being total recluses to the boldest fish in the tank. This small 60 litre tank contains mainly tetras, 12 Neons, 2 Black Neons, 4 Cardinals, 2 Black Phantoms and 2 Rummy Nose plus one male guppy. They all shoal and mix together happily, even the guppy. Incidentally, the tank is 120% overstocked according to the calculators but they have been in there for over a year with no problems at all with only a standard filter and minimal water changes, though with lots of, live plants.

What has this to do with the question? I reckon that if you had more similar fish (i.e. more tetras) in the tank, they would all be more confident. These fish all live in large shoals in nature and the more there are, even if not all the same species, the happier they seem to be.

It's possible your fish had spent all their live in bright light e.g. at the fish shop and then you brought them into another brightly lit environment to which they were already accustomed. When the lights were off they had their first taste of the conditions they really like and want more of the same! That may be nonsense, but I can't think of another explanation.

I'm not sure how big your tank is, but Glowlight danios, and other danios, need a minimum 80 cms length, preferably more. It's a bit of a myth that they are surface fish and they would probably use all levels of the tank. The only danios I have are Zebras and Pearls and they spend much more time near the tank bottom than the top. Apart from the obvious bottom dwellers, such as most catfish, I think a normal aquarium is too shallow for fish to clearly stratify into top, middle and bottom fish. Very few fish, maybe Hatchet fish (which need big tanks) actually normally stay near the surface. It's a pretty dangerous place in nature, you can be attacked from below by fish and from above by birds! 
Of those you mention I'd go for Harlequins, though I think almost any fish from the tetra or rasbora types would be OK as they tend to have similar temperaments. You only need to avoid the sometimes more aggressive types such as Serpae tetras.
 Fish swimming actively round all parts of the tank is not necessarily a good sign, happy fish will generally be more relaxed. Most of mine have adopted particular areas as their own and spend a lot of their time there.

Java fern is the live plant I started with, the only one I couldn't kill. Looking at the photo of your tank, you could attach it to the piece of wood and the rock-like thing on the right. You just need to tie it on with a length of cotton or nylon thread till it clings by itself. I've also heard of elastic bands being used.