Possible Changes To The Tank - Thoughts Welcome

As a further update, I was planning to wait until 24 hours had passed, and, if the situation hadn't improved, remove the extra "furnishings". However, I've just come into the fishes' room (aka the living room) and... drumroll... all 6 tetras' tails are now red in colour after 23 1/4 hours. There's some more natural-looking behaviour taking place, such as the female tetras foraging for and retrieving their breakfast from the substrate. Behaviour is not "normal" or relaxed but they're taking turns in swimming out nervously in groups of 2 before returning to their original position, then the next pairing swims out a bit further and returns, etc - all at a more usual position in the tank rather than up and down the glass or near the water surface.

I think I'll leave all "as is" for now and keep monitoring the situation.

Advice re the Vallisneria, as per previous post, would still be appreciated; thanks.

I don't see any reason why the vallis wouldn't grow in a pot, why don't you want it in the substrate out of curiosity?

I just have a sand substrate ie Unipac's Tana sand. I'm assuming I'd need to change the substrate if I were to plant the vallis in it, and I think it's abundantly clear from the fish that they just don't like upheaval/changes of any sort!

@Littlefish - very helpful indeed; many thanks, LF!

[Update: progress in the tank - more courage, activity and normal behaviour including swimming through the java fern or hiding on the other side of the java fern and keeping a watchful eye on me through it, as though a threatening glare not to lift the lid of the tank and do anything else for a while yet...]

Over the course of yesterday afternoon, the situation improved considerably to the extent of near-normality resumed - and, major newsflash - we actually have light which is being tolerated, something I thought I'd never, ever witness! I put the light on to take a photo, conscious that I was subjecting the poor souls to even more trauma than they'd already been through but intending it to last only a minute or two, when I discovered that they were actually unperturbed by it, instead of the usual, terrified reaction. Maybe, after 23.25 hours of stress, they've worn themselves out and are prepared to tolerate anything..?!

Hidden in the background include a piece of bamboo embossed in java moss (leaning against the original piece of redmoor wood, a moss ball sitting on top of 2 terracotta pots, and, on the right hand side, the additional piece of redmoor wood with an extremely amateur attempt of java fern (left), java moss (middle) and anubias (right) wrapped around it. Silk plants have been pushed towards the back. I'm under no illusion that the plants will survive, given my reputation with household plants. However, time will tell... Going to get some vallis next; thanks for that tip about it being ok in sand, @Fiona.

Photo taken deliberately close to spare Sue (and anyone else) from the 'trauma' of seeing the low water line while I'm still using the original filter. I'm aware folk probably think the tank is still too sparse but I can experiment a bit during the weekly water change with positioning of silk/live plants, etc.

Thanks, @Richard W - I'll monitor the situation over the next while and, provided that the fish continue to tolerate the light*, and, depending on whether or not I manage to keep the live plants alive, I'll think about replacing them with more realistic silk or live green alternatives. With no tank light on for the past year-and-a-half, the tank looked very dark and so there was a need for some colour in it; however, if the tank light can now remain on, then it opens up opportunities for less garish silk plants and more options for live plants. That purple-coloured one on the left is a big favourite among the harlequins, though - the two little harlequins enjoy nesting in on the leaves, while the others have started using it for mating in.

[* I appreciate what you're saying about "tough love" although it seemed at various points that I was going to drive those fish to a very premature and sudden demise due to the stress of the new addition to the tank. Let's hope they remain unscathed from the experience.]

Thanks, @Littlefish

I did "cheat" slightly - the bamboo embossed in java moss was bought like that , purely so that I could have a template to copy, of course.

Imagine how much fun they'd have in a vallis forest, the stuff slowly spreads via runners, I just cut them off and replant them when they're large enough.

and congratulations for persevering with the light 

Thanks, all.

Hopefully the vallis will be purchased and in the tank by the end of the week, after which I'll provide a further update.

Floating plants probably wouldn't work due to the (spare) filter in the tank which causes the water surface to move in circular fashion round the tank albeit gently. Are there any floating plants of which the roots could be gently tied/wrapped around the top of some wood ie which would float on the surface but which would have sufficiently long and flexible roots (maybe 10cm +) to keep the plants in place by them being tied to wood?

@fcmf do you have a timer for the light? I think they are quite cheap on Ebay

The frogbit in some of my tanks circulate with the flow from the spray bar. It doesn't seem to have any adverse effects. Last week I saw one of the amano shrimp clinging on to the underside of one of the pieces of frogbit , riding around as the plant went with the flow. I don't know if the shrimp thought it was some sort of Alton Towers style ride, or if it was too busy picking at the frogbit to even notice that it was going around.