The chap I bought the RSM 130 from told me about Marine 23 aquatics, which is on a small industrial estate in Cheadle Hulme. It's within spitting distance of the Stanley green trading estate where there's a Screwfix I've been using while decorating and fixing my new house.
As I needed salt anyway for this migration to the RSM, I popped down there. It's literally a converted self storage unit, not very elegant at all on the outside, but inside is a different story...
It's relatively new, just over a year old, but with big plans of expansion into the other adjoining storage units. They do have a huge tank with Koi carp for sale which is confusing, and also a decent sized freshwater selection, but it doesn't encroach on the marine side at all, the place is pretty big.
The marine fish are all in appropriately sized tanks, with tiny cubes for tiny fish, but a big selection of weighty Tangs, Angels, etc in a big well lit 'centrepiece' tank up above the smaller tanks around. There's shallow coral tanks with fist sized SPS colonies for £45 or 2 for £80 IIRC.
There's a sofa and small kids area, and as we had our two in tow, we were asked permission, then kids offered sweets, which was a pleasant touch.
They do a great loyalty scheme, where members get a nice credit card like membership card, get 10% of everything. There's something about over £20 as well, but I can't remember that, but got 10% off the Red Sea Coral Pro bucket I bought and separately, got 10% off a £2.99 pack of Mysis Shrimp.
The staff seem genuinely great, you can see true enthusiasm in them, there's not an ounce of 'here for the paycheque'. Not at all pushy, just very approachable and no typical retail bullshit 'is there anything i can help you with today?', just nice guys.
I'll definitely be using them again as they're only 3 miles from me, and since I moved away from the city centre, Oasis, Cockfields etc are now too far to be worth bothering with, plus the loyalty scheme is a genuine great benefit.
Not that it'll benefit me, but they do free delivery on saltwater and/or RO water too within 10 miles, literally as many litres as you need, they have thousand litre tanks on a trailer.
A young company doing everything right deserves every bit of positive reviewage it can get, and people on the 'net generally only ever leave negative reviews, so thought worthwhile leaving a bit of an intro for them combined with an overview of a positive experience.
For a look around;
(no this wasn't paid for in anyway

I even invited them here, the guy wrote the link down but they've not arrived yet, but are welcome)