Right, so I've got my tank tonight. I've measured the tubes that are in there already, they are around 41 inch.
Also, I've attached a photo, these are what I thought were serpea tetras but I'm not too certain now. Thoughts?
Light first. This is good. The tube I would recommend is the Hagen Life-Glo T8. There is a 107 cm (42 inch) at 40 watts which is likely the one required. If you can find a store locally that carries these, you might be able to try one (sometimes stores will allow you to return if they don't fit). Two obviously. I use this tube on all my single-tube tanks because frankly there is simply none better for colour rendition, intensity and spectrum.
I believe you are in the UK so I don't know how common the Hagen "Glo" series is; just make sure they are T8, not T5 which they also manufacture but which won't fit T8.
There are other tubes in this series, some terrible, some less so. I tried the Sun-Glo once, in combo with a Life-Glo, but it didn't impress me. Do NOT get the Aqua-Glo nor the Power-Glo. The Flora-Gro might work in combo, I have not tried this one in the series. It will lessen the intensity though, and over this tank the two Life-Glo will provide more light (but not too much). So I would recommend two Life-Glo.
Now the Serpae Tetra. I cannot tell much from the photo; here is some data I wrote on this species.
This species is closely related to some 30
Hyphessobrycon species known as the rosy tetra clade that includes
H. bentosi, H. rosaceus, H. megalopterus [Black Phantom],
H. sweglesi and
H. erythrostigma ["bleeding hearts"] to name but a few. It shares the common traits of a black dorsal fin and a dark (in this species black) humeral or shoulder blotch immediately posterior of the gillcover, and (usually) a red body colouration. The shade of red varies on fish from different geographical regions. The dorsal is edged in white. This species is readily discerned from all the other rosy tetra species by the dark colour pattern on the posterior part of the anal fin that expands from the black distal (furtherest from the body) border of this fin. Weitzman & Palmer (1997) note that this dark pattern is somewhat variable on wild-caught specimens from different locations.
Many of the fish now available in the hobby are commercially raised and differ from wild-caught fish with respect to the dark shoulder or humeral patch. [I cannot discern one on the fish in your photo.] Commercially bred fish are descended from hybrids (perhaps unintentionally) of fish from different geographical areas, and the patch is shorter or all but absent on most; on wild-caught fish, this patch is black, elongate and slightly triangular.
This fish has gone through several name changes, being placed in four different genera before being assigned to
Hyphessobrycon by Weitzman & Palmer (1997). Within this genus, the names
H. callistus and
H. serpae are now recognized as synonyms of
H. eques and not valid distinct species; fish still appear in stores under these synonyms.
Behaviour can be unpredictable; keeping the species in large groups and in larger tanks tends to lessen its aggressiveness. This variant behaviour, like the anal fin pattern mentioned above, may also partly be due to significant variations between the fish. Dr. Stanley Weitzman (1997) has suggested that the "species" may be a complex of closely related species that are geographically quite variable and occur over a wide area of Amazonia; it is quite possible that this "species" may actually be several different species, each endemic to specific river basins; this will only be ascertained after collections from many locations have been studied in detail.
If the store labelled these as Serpae, or Red Minor, they probably are
H. eques. They do not make good tankmates for slow, sedate fish or those with longer fins, as this species will very readily fin nip other fish to death. How many do you have? It might be an idea to leave these out.
