Update:
I removed the spray bar and it's made a world of difference to the flow: the single outlet is submerged about 10cm below the waterline and slightly angled toward the back of the tank. This is creating quite a strong flow in a clockwise direction around the aquarium. The floating plants are getting bunched up in pockets of flow though, which is unsightly.

I may remove the hornwort (it keeps sinking) but leave the frogbit.
Maybe it's a psychological thing but seeing a flow in the tank makes it look healthier. It's not strong enough to blow plants sideways but many of them are swaying pleasantly. I don't know how strong the current would be for all those small fishies though! I'll have to wait and see. I could point the flow upward but then I'd have greater surface agitation, which I'm trying to avoid.
I installed my Fluval CO
2 88 (which I got for a good price). It's so easy to setup and looks great. As it happens, the new flow from my outlet catches the CO
2 micro bubbles and spreads them out and across the tank. I noticed another algae bloom yesterday so I concluded that the tank is just getting too much light! So in this delicate settling-in period I've covered the thing in thick black towels. I will then allow 5-6 hours of light + CO
2 when I come home. (If I decide to stick with the Fluval system I think it would cost me ~£10/month, which is far less than I spend on wine

But, this is only an experiment and I'm sure there are much cheaper solutions.)
Remember that I dosed a tiny volume of ammonia yesterday midday - remember that! I had a final batch of plants (crpyts) to plug into my tank followed with fert sticks. I also repositioned a java fern (I think it is!) from the substrate (noob) to a bit of wood (pro). I've taken a few pics which I'll post in a bit (keep checking back!)
I also trimmed any bad leaves and did a tidy up. So I had my hands in the water quite a bit. I stood back and admired my handiwork - pleased.
Then it was onto the existing 70L tank for maintenance. I emptied 50% of the water this time and gave the gravel a good hoover. I've treated the fishies recently to daphnia and tubifex (which was a wonderful experience! I've never seen them all congregate together and feast so hungrily!) - but the results have been egregiously manifest on the gravel! I will say no more

Actually I will say one more thing: how can something so small poo something so big?! Extrapolating to human terms, I would be on the toilet for 3 weeks... (Too uncouth for this time in the morning? Apologies!

)
I gave the filters a good squeeze and replaced the filter, with one major exception: because this 70L is overstocked and underplanted, I purchased a small amount of Seachem Purigen which sits in a micron-hole bag in the middle in the filter. This is the stuff which adsorbs nitrogenous compounds; it's also supposed to be a water polisher and clarifier. In this tank I don't care if it competes with the bacteria because these fishies will be moving house soon anyway. I had some surplus live plants which I decided to put into this tank too. All finished, tank water replenished. Fishies were massively spooked by all the commotion so I left the lights off so they could relax for the evening.
I should add that between tanks I always wash my hands. But when I sat down to relax I noticed my fingers were burning, especially on my right-hand - the hand which had predominantly been in the 185 tank. Lots of washings didn't ease the pain. It wasn't excruciating or anything, just unpleasant. My figures looked cracked and dried. There's a few possibilities: the carbon solution (which isn't carbon at all but a formaldehyde variant!) or ammonia in the water. Now, this hasn't happened to me before and the ammonia dose was tiny - but clearly there was something caustic in the tank water. Either that, or it was caused by something else (I made a hot curry that evening with three green chillis...) and the tank was a coincidence? I don't know. But I offer it here in case anyone has experienced the same. Really, with such a tiny concentration of ammonia in 185 litres it seems unlikely but it's the most plausible explanation.
At least now I know: don't play with the tank unless ammonia is zero!
My hands are fine this morning, but the skin under my fingernails is still quite sensitive. I'll survive.
And there we are: the longest fishy update in human (and fish) history. Probably no one cares, and is only here for the readings!

Well, I haven't made any this morning! Perhaps at lunch-time.
Pics to follow.