Ideally, each adult frog you have should have 10 gallons of water each, with space to swim, hide and rest on something at the surface. They will spend most of their time moving around in the lower areas of the tank so length is more important than height when choosing an aquarium.
Water Temperature & pH
Because they are fully aquatic and constantly exposed to the water they quality must be good otherwise you can expect bacterial and fungal infections. Saying that, they are relatively forgiving if you miss a water change. The water temperature should be set between 68 and 75 degrees fahrenheit (20 to 24 degrees celsius) - they are temperate frog so prefer the lower temperatures in this range. but can tolerate a few degrees either side. The pH of the water should be 6.5 to 7.5. This can be checked using test kits that you can buy at your local aquarium shop.
Lighting & Filtration
Lighting is not strictly necessary but the frogs won't mind standard aquarium lighting. Note that the lights should always be switched off at night so that the frogs can exhibit natural day and night behaviour cycles.
30% of the water should be changed weekly.
Filtration is really important as the frogs will be healthiest when kept in good clean water. The best type of filter for these frogs is an external one as they are sensitive to vibration and will become stressed with prolonged exposure. External filters aren't too expensive and will keep the water very clean. When setting up the external ensure that the intake pipe has an appropriately sized guard so the frogs can't get sucked up or stuck in the piper. Position the tube that returns the water to the aquarium against the glass to minimise water disturbance.
If an external filter is not available Internal filters can also be used but should be switched off during the night to avoid vibration stress.
Substrate, Decor & Plants
There is a lot of debate about which substrate is the best to use with these frogs. There are several options :- sand, gravel, pebbles or nothing.
Sand can be used for all sized frogs and is relatively safe but harder to clean. Gravel should only be used if it's too small to become lodged in the digestive system or if it's too big to swallow. Pebbles are safe to use and a tube can be used to suction off any waste from between them. No Substrate = no risk of ingestion and very easy to clean, but not very natural for the frog.
In my opinion sand or pebbles are the best substrates for African Clawed Frogs.
The frogs will instinctively hide when they feel threatened or want to rest, so it is important to provide hollow ornaments, bog wood, large flat stones (make sure they are secure) or dense areas of plants so they can do this. Avoid sharp objects that may injure the frog.
All varieties of aquarium plants are safe to use with ACF's but be aware that the frogs may rip and uproot tender varieties. Silk plants can also be used but I would avoid plastic ones as they can get snagged on the webbing between the frogs toes and cause injury.