Okey doke
I own a 60 litre tank myself so am reasonably familiar with it's size. Sadly, it is not big enough for angelfish, as they require 18" minimum height requirement, because they are big fish that get taller rather than longer.
An RTBS, as you have learned, is an aggressive fish that is willing to bite and chase other tank mates. This isn't very good for either the RTBS or the fish it is chasing, as stress is a big fish killer.
Sucking loach? You haven't identified what this is. Is it one of these -
or is it more like this -
?
3 Kribensis is pushing it by far in a 55 litre. Kribensis require 10 gallons each, are aggressive towards other tankmates when breeding, and are also aggressive to their own kind! Often people will have to seperate a pair because the male is attacking the female or vice versa. Kribs need a 20 gallon in order to stake out a territory. These requirements, plus the shark, make them unsuitably housed in your tank.
So, we've established that the tank is too small, which leaves you with the option of rehoming the fish, or, getting them a bigger tank. Keeping them as they are is not an option, as they will end up stunted, and inevitably live short stressful lives.
So, if you want to upgrade, and keep all the fish (this is ignoring the algae eater right now, which I am labelling unidentified), what size tank are you going to need?
A popular sized footprint for an 18" high tank is 48x12x18. I myself had one of these for goldfish, and it was a great tank. 45 US gallon, which makes it better for all the fish involved. I recommend you keep only 2 Kribs however, a male and a female. Keeping 3 will lead to one being bullied or shunned while the others pair off. I know you are drastically avoiding rehoming your fish, but this is the only way possible to make the tank inhabitants healthy and happy IMO.
The RTBS will have plenty of time to get big in the 45, plus, the angel fish will be able to grow long also.
Are you any closer to knowing the algae eaters identity?