Possible Changes To The Tank - Thoughts Welcome

Where are you thinking of sourcing your darker sand from?? I can never seem to find cheap sand that isn't really light in colour and it just looks so fake to me. I have also considered mixing them to reduce brightness...

I notice that my LFS has this https://fishkeeper.co.uk/product/aqua-range-aqua-substrate-black-sand-20kg and this https://www.jbl.de/?lang=en&mod=products&func=detail&id=5011 in stock. My current sand, bought from this LFS in the past, comes from this range http://www.unipacpet.co.uk/aquatic/aquarium-sand/- you'll see the Limpopo sand is its darkest (while I currently have the Tana sand). I found a thread on alternatives in the past as the original poster had made the same comment as you - will try to dig out the suggestions from there and let you know, @Matt, but my vague recollection was that there was no consensus on which seemed the least fake.

I know that in the past I have bought 3 brands of dark sand, and one of them did feel quite sharp, so I didn't use it.

If you/anyone has fish that like to forage in the sand, I would exercise some caution with choice of substrate. In the past, I had problems with 2 of my goldfish (in separate tanks) ingesting gravel stones and choking on them, taking several hours to release them (cough them back up) - this happened one time to many, so I converted to a sand substrate in one of the tanks. The sand substrate ended up being ingested too, leaving a large pouch forming on the side of my fish's abdomen and massively thick sandy poo passing out which looked ever so painful, and ultimately I ended up having to opt for a barebottom tank. Thinking back to all of this, I'm semi-minded now to keep to what's working - my two female tetras have a habit of foraging and grinding on the sand pieces before spitting them out but thankfully this doesn't seem to have caused any problems (yet) but I wouldn't want to find that a change of substrate might bring problems with it.
 

I bought some limpopo sand a few years ago and never used it. I tested it with vinegar and it fizzed. It looked just like finely crushed, dyed coral. But I understand from elsewhere that the company has changed it since I got mine and it no longer affects hardness and pH.
When I replaced the sand in my 180 litre tank this summer I looked round for dark sand but failed to find any that I liked. There were black sands but they all felt sharp and granular rather than small and smooth like the sand I had, which I got again.
I would strongly recommend looking at any sand in person before buying, even if you then go on-line to buy it cheaper.

Just think, you doubted your ability to grow live plants, and here you are a few months later with a tank full.
Brilliant. 

am i right in saying you have low powered light on this tank?

The tank came with a Sun-Glo light but the light I actually have in it is an Aqua-Glo light https://uk.hagen.com/Aquatic/Lighting/Fluorescent-Bulbs?brand=glo [NB a light tube, not LED].

[Here's the background to the lighting: http://forums.thinkfish.co.uk/general-fishkeeping-advice/advice-re-change-of-lighting/ Oh my goodness, how different and bare my tank looked two years ago!]