The tube leading up to the filter is gettind pretty dirty - should this be cleaned or is this beneficial bacteria as well?
If it is easily taken off during the weekly water change, rinsing it out (you can get a filter cleaning brush, or an old manual toothbrush may work, depending) won't hurt. I must confess to leaving my canister filter hoses for longer than i probably should, provided the water is easily getting through.:lol:
Regarding the silver sharks, they are silver bala sharks. I'm aware that they can grow pretty big but was under the impression that this would take a long time and that they would only grow based on their habitat - is this not true
No, it is not true. Fish grow constantly, both externally and internally (organ development). When the tank is too small for the fish, stunting can result; this means the internal development is abnormal and down the road the poor fish has health problems it would not otherwise have, and usually early demise (shorter lifespan). The physical space will retard the fish's external growth too, so this may be how the fable about fish growing to the tank size arose; way back then aquarists had less scientific foundation that we now have.
There are two components to tank space. One is the physical space the fish "needs" to be itself, and this has to increase [or be large enough to begin with] as the fish develops. Second is the water quality; fish release pheromones and allomones and these have to be diluted and removed, since they affect the fish itself and other fish in the species (pheromones), and other species (allomones). These chemical substances can also stunt the fish, and stunt other fish, and several other things too.
The Bala Shark is in our profile [are you familiar with the profiles?], click the shaded name for the profile. It gives the minimum tank size and the number of fish in the group where this is relevant, as it certainly is here. I won't repeat all that the profile says, so please have a read.
I recently added a few cherry shrimps to the tank to help clean it up and the silver sharks seem quite keen on those, although the shrimps are a bit too quick for them, however I haven't seen as much of the shrimps as I'd hoped to, they seem to be hiding in my shipwreck ornament away from the sharks and don't come out very much - is this normal? Are they not compatible tank mates?
As noted in the profile, the sharks will eat smaller fish. And crustaceans are a natural food item of almost all tropical fish. The shrimp will not likely win this game.