Ooh, that sounds lovely. Will it be in an internal wall viewable from both sides or will it just be viewable from the front?
I wouldn't go any small than 60 litres. If you go too large then you'll need to allow extra space underneath for an external filter or a sump. I'd probably go for around 80 or 90 litres which is big enough to leave you plenty of options for fish but small enough to be manageable. This would be around or just over 3 feet long depending on the height of the tank. It'd be preferable to have length over height because the surface area will be larger (important for oxygenation).
You'd need to speak to a builder about the weight of it. A gallon of water weighs 10lbs so 90 litres would be about 190lbs/86kg and then you'd need to add extra for the glass. Acrylic is lighter but more expensive. You'd need to get something made especially because tanks usually come in standard sizes and most are deeper than 40-50 cm.
You'd need to leave a good 6 inches of space above the tank to allow access for cleaning etc.
Thanks Eau! Yes, we'd like it to be viewable from both sides. I went into London Aquatic today for a chat. The guy I spoke to said that longer and shorter is better - looks nicer, don't run into problems of needing thicker glass to cope with the increased water pressure, and easier to clean (unless you have extra long arms). He said custom made and that we'd need a steel frame to set the tank on. He said we'd need to leave the entire space underneath free for the pump (sump not cannister?) and other gubbins. We're planning on having kitchen cabinets above the tank, with completely removable base and bottom shelf, so that should be OK for access.
It's really helpful to have an idea of manageable size - the guy in the shop kept saying that I could have it as big or small as I want, which is not that helpful when you don't yet know what you are doing....
Sounds like he knows what he's doing! Yes, you could have a sump or a canister filter underneath- this would be a must for larger tanks. If it's a smaller tank (like a 90 litre) then you could have an internal filter. You could disguise it with plants etc but it would be tougher to hide in a tank that's viewable from both sides. It depends how fussy you are about whether you can see equipment.
You could go larger than 90 litres if you wanted- how much time do you have to maintain it?
DH has just got home and says he is thinking of a 1 metre long tank that is 25-30cm high and 45cm deep. Is that tall enough for fish? He says can the pump and gubbins go above the tank (we could just dedicate one of the kitchen cabinets above to tank stuff) or does it all have to go underneath? Is a tank that size a major PITA to maintain? Really appreciate your input! Thank you
If you're having an external canister filter then it needs to go underneath because it's gravity-fed. Other stuff like the lighting unit, air pump etc can go wherever- if you're having an air pump, don't forget to fit a non-return valve to the airline to stop the water going up it.
That tank size comes out at 130 litres- definitely within the realms of manageable! It would take probably around 30 mins- 1 hour to do a water change once a week and then a few minutes here and there to tidy up plants, do a bit of algae scraping etc.
Got a probably daft question for you - does the pipe leading to the canister/sump pump go up and over the side of the tank?
The guy in the shop thought sump pump would be better than canister (less risk of leaks, easier to change to marine if we chose to, easy to chuck whatever stuff we need to chuck in the water in). Would you agree?