I've taken on my neighbour's fantail goldfish as they're emmigrating, however, when they bought the fish over, they also brought this creature. Sorry the pictures aren't great, I can't seem to get a good image from the bowl. General description: about 2inches long from tail tip to head, stays mostly on side of tank, but has been seen on filter at the bottom. Very fast. Dark stripe on otherwise clear tail, undercarriage 'transparent' - I can see it's little heartbeat, upside: silvergray with dark speckles.
I was told it ate the algae, however after doing a bit of research I'm a bit concerned that it's going to grow to be far too big for the Biube that it lives in. Also, do I need to provide food?
It's a hilstream loach and despite shops selling them as algae eaters to go with goldfish they require a completely different and specialised setup. Not at all suited to a biorb (but then neither are goldfish.)
A biube isn't quite as bad as a biorb but the basics are 1/ Volume. A fancy goldfish needs a minimum volume of 120L. 2/ Surface area. Oxygen disolves into the water at the surface. Orbs and Ubes have relatively small surface areas. This means less oxygen. Oxygen deprivation weakens the fish causing problems with development, digestion and the immune system. 3/ Filtration. Undergravel filters are very old technology being inefficient Reef One's design compensates by adding expensive absorbative media which needs to be refreshed regularly or the fishes toxins may not be removed from the filter. 4/ Poor use of space. A square tank gets much more water into the same space as a spherical one.
Goldfish being large, messy fish with a high metabolic rate (ie they breathe and poop lots) need a large volume of water, large surface area and excellent filtration. They're also sociable fish so do better in small groups. Really a starter tank should be no smaller than 120L and have a surface area at least 90cm x 40cm or equivilent.