We acquired 2 funfair goldfish , pets at home said this fish that is on the top of the bridge should be ok and the goldfish shouldn’t be able to eat it! The problem is it keeps chasing the goldfish and trying to suck/ bite them- should these be in the tank together?
What is the type of fish that you are referring to, besides the goldfish? You'll need to know what type of fish you're keeping, so that you can ensure that you meet its/their requirements in line with the species profiles at https://www.fishkeeping.co.uk/modules/caresheets/
Please can you post a photo of the fish and also let us know: * what size (dimensions, volume) of tank the fish are kept in * water quality just before your usual scheduled water change (i.e. ammonia, nitrite, nitrate) * water parameters (i.e. your postcode's water hardness levels in CaCO3 or German degrees hardness, as per your water/utility company website) ...as these may affect fish behaviour. Thanks.
If it is harassing the goldfish, and particularly to the extent you describe and which could result in stressing the goldfish to the brink of injury, illness or death, then it needs to be separated from them. Your priority will be to establish which of the above it is, and, if a Chinese/Siamese algae eater or similar species which requires a much larger tank, then either upgrade its tank ASAP or else re-home it via www.aquarist-classifieds.co.uk
As it's difficult to tell from the information you've provided, and without the water quality and water parameter information, my inclination is that the fish is more likely to be a Chinese/Siamese algae eater than an otocinclus as the behaviour seems very different from the timid/gentle behaviour of an otocinclus and which would likely be intimidated by the presumably larger goldfish.