Think I've got the hardscape for the divided 15 gallon sorted. I'm using Dennerle 9 in 1 substrate with black sand on top, then various grey speckled and white pebbles, rocks, a flowerpot and fingerwood driftwood pieces. The dividers were a pain to make because apparently it's impossible to find plastic cross-stitch material in the UK - go figure. I couldn't find a long enough piece for the back so had to overlap a piece, but it's all held together pretty well with the binder spines and held firm to the tank with notches in the plastic that fit snug to the rim. There's a 100W heater along the back of the tank behind the divider and the space is filled with gravel and will have cycled filter media to quick cycle the tank and just provide more places for the BB to live when I get the thing filled with water, so I'm only using one plug to heat the whole tank. I'm going to use sponge filters in each divided section run off one pump. The two dividers making the three sections are sewn onto the back divider with nylon invisible thread and then reinforced at the bottom and the glass side with binder spines. I'm going to make a lid with two slots to hold the two in place as well to make it doubly firm because they're a bit wobbly at the moment and I don't want any slip-throughs. Planning on heavy planting, especially in the middle section where the decor is lower.