Aquarium Systems Test Kit A new range of test kits from Aquarium Systems that accurately test your pond/aquarium water. Test kit by Aquarium systems for measuring the total hardness of your tropical or cold freshwater aquarium. Comprises 2x 10ml GH indicator fluids - the number of tests the kit will perform will vary according to hardness levels. Differing levels of water hardness (GH) will be required depending upon the type of fish being fish being kept - your tank must be adpated to hard (eg fish from Lakes Malawi or Tanganyika) or soft (eg SouthAmerican) water species, and the level measured to ensure stability.