Ancistrus size depends on the exact species, but around 5" total length for the "common bristlenose", which is the one that you'll find more easily in the shops. Costs about a fiver or so.
Most of the peckoltia's grow to about that size too.
Ancistrus is a pretty good algae eater, and they aren't expensive either (because they are easy to breed. I've got 25-30 little ones swimming about in my tank at the moment, with the male sitting on a clutch of eggs for another week or so, for the next batch of 30).
You can keep two Ancistrus in your tank without problems. Just make sure they have plenty of hiding spaces (the more hide-aways they get, the more likely it is that you see them out, because they feel safe if they are able to hide quickly).
Note that Common Pleco and Common Bristlenose ARE NOT the same thing. They may look somewhat similar (they are both Loricariid's).
Common bristlenose is dark brown (going to almost black on young ones) with lighter spots (almost white on young ones). Males will have bristles on the front of the head (hence the name), and sometimes the females have them too.
Common pleco will have a brown base colour with a darker spot/line pattern (of course, common pleco is used for about 6 different species, so it's hard to be specific onthis).
The common pleco will grow to large (12"+) size if it's given good care (like good water quality and food). Also, once it grows a bit bigger, it's not such a great algae eater.
Will keep the plec for the moment, its good that i can take him back at any time, im rather attatched to him already hes gone into the tank and is just a great character already!
Oh, all Loricariid's (the whole family of about 600-1000 species) are great characters, all in their own way, from the ones that grow to just over an inch to the ones that grow to over 3 feet...
I realize I missed a couple of the answers to your questions: Mine are what the cat-elog describes as "Ancisturs sp(3)", which is a specie of ancistrus that are commonly tank-bred, and seen as "the guppy of the Loricariid's". As long as the tank is reasonably well-kept, you get a male and a female, they'll spawn. Unfortunately, the first spawn failed due to "greedy fish" (i.e. Freia the goldfish ate the babies...).
I'm hoping the ones that I've got now are going to grow big enough to trade in the fish-shop for a couple of fish or a portion of live food, or whatever it may amount to. I'm by no means a professional breeder, but there are some on this forum (found in the Loricariid section) that do professional breeding of "Common bristlenose".
As the young bristlenose sell for about 3-5 quid in the shop when they are about 1.5-2" long, and mine are currently shorter than an inch (about a month on from coming out of the cave), I don't think I'll make any money on keeping them for three months and then selling them...
Just buying the vegetables to feed them will cost as much as I'll get for them, I'm sure. They currently go through a slice of courgette or sweet potato a day, plus one or two algae wafers.
But with a potential of about 60 of them at 1.5" in a few months, I'm sure I'll have to get rid of them someway. Eventually all your friends that have a fish-tank will already have one, and it's getting difficult to keep them all... I'm already having to plan for how many I can keep in which tank, as I don't have a specific "grow-out tank".
My bristlenose tank have danios in it. They are unfortunately pretty good at eating their own eggs about the same rate as they are producing them. Mine spawns (at least they behave like they are spawning) all the time, but no fry yet after about half a year of spawning at least twice weekly... That's pearly and zebra danios.
The "Common bristlenose" is not hard to get, every fish shop has them (or can get them), so if you want some, you should be able to get them from your local.
They will carry eggs until they meet a suitable father/sperm donor that does the right dance routine... Highly technical answer to highly techie questions, eh?
But honestly, they will look quite fat (the technical word for this is "Gravid") for a long time if they don't meet "the right guy". On the other hand, if you have any male in there, that should be sufficient to satisfy the "right guy", they aren't supposed to be very picky...
well i have 2 fat females i think and one very slim what i presume is male!
Im so new to this i have NO idea! lol
I'll just see how they go for the moment, they have all been acting very strangly over the last day or 2, the 'male' has been chasing the bigger female everywhere, bashing through the neons and scattering them!
I thought this may have been the 'dance' but maybe not!