their full name is Otocinclus species, they are usually O. affinis, but there are least two others. People usually call them "oto"s for short.
Don't get them just to remove algae. Once they eat the algae, they go very hungry and require supplemental feeding. They don't eat usually prepared foods (like pellets, wafers, flakes), so are difficult to feed. They are also very sensitive to water quality.
I say, just do a little work and scrub it off. Also, figure out what's causing the algal growth. Are you changing water often enough? What's your bioload (what's living in their)? Is it overstocked or are you overfeeding? The last two will usually result in too many nutrients for algae (nitrate, phosphate). You can reduce the amount of nutrients through frequent water changes.
besides, it sounds like your tanks are having issues with stocking/aggression, and possibly illnesses (BAC killer), i'd say you need to settle those before you get any more fish. ESPECIALLY an algae-eating fish. they're a lot more trouble than most people appreciate.