Original sentence: Aquarium stores will often use a 6-7 inch piece of plastic pipe for this purpose.As with most scale-less fish, they are  prone to external parasitic attack.Captive knife fish often display aggression towards one another, and differentiation between sexes is near-impossible without dissection.Due to their weak electric discharge, a close, contained group of knife fish (as in an aquarium) will line up side by side.In the aquarium Black Ghost Knife Fish will eat carnivore pellets, bloodworms and feeder fish.It can be very motionless during daylight hours.It needs a hiding place such as a cave.Knifefish will often fight if there is more than one.The black ghost knifefish is  a very hearty fish that can do well for many years in a large enough tank.The fish will not care if the pipe is clear or opaque.The most common is Ichthyophthirius multifiliis, which resembles white spots.These fish require a minimum tank size of 75 US gallons (280 litres) once full grown, due to their large size.They have been known to jump from aquariums, so a glass top is recommended.They prefer highly oxygenated air pockets and may spend much time reversing into "bubble walls" made by air filter stones.They prefer water with a 6.0 - 8.0 pH, a water hardness of 5.0 - 19.0 dGH, and a temperature range of 73-82 F (23-28 C).They will also eat peas, earthworms and frozen community fish foods.They will eat other very small fish in the aquarium
Edited sentence: As with other scaleless fish, they are vulnerable to parasite infestations such as ich (Ichthyophthirius multifiliis).Black ghost knifefishes require a large tank of at least 280 L (75 US gal), and should be provided with a shelter (such as a plastic tube) in which to hide.They will eat smaller fish in the tank and are intolerant of conspecifics