Regent theoretical interest in Kagomé antiferromagnets arose from the prediction that they possess a new type of magnetic ground state in which there is no magnetic long-range order even at T = 0. Prior to this work no detailed investigations had bee made of the magnetic properties of real materials that provide models for this class of magnet. Members of the series AB₃(SO₄)₂(OH)₆ (A⁺ = Na⁺, K⁺, Rb⁺, Ag⁺, NH₄⁺, and H₃O⁺; B³⁺ = V³⁺, Cr³⁺, and Fe³⁺) have been studied using a combination of experimental techniques- ac and dc susceptibility, specific heat, neutron diffraction, and MuSR. The hydronium compounds (A⁺ = H₃O⁺; B³⁺ = V³⁺, Cr³⁺, and Fe³⁺) have been shown to provide the best model Kagomé antiferromagnets with S = 1, 3/2 and 5/2 respectively. (H₃O)Fe₃(SO₄)₂(OH)₆ has been shown to possess only short-range magnetic order with a correlation length of 19 ± 2Å, below a spin glass transition temperature, T_f ˜17K. Unlike normal spin glasses, muon spin relaxation measurements show that this magnetic phase is dynamic below T_f (H₃O)Fe₃(SO₄)₂(OH)₆ is a spin fluid: its dynamic and thermodynamic behaviour are completely unlike those seen in normal spin glass or long-range ordered ground states; the specific heat varies as T² below T_f, rather than the linear T dependence observed in canonical spin glasses. Deliberate reduction of the concentration of magnetic atoms destabilises the spin fluid ground state and induces the formation of long-range order of the type seen in the other less magnetically concentrated members of the series. This is the first example of a system in which diamagnetic dilution causes it to order classically. (H₃O)Cr₃(SO₄)₂(OH)₆ has a broad transition to a dynamic short-range ordered state at ˜ 30K, similar to that seen in (H₃O)Fe₃(SO₄)₂(OH)₆, but with no observed spin glass behaviour. A weak ferromagnetic transition at 2.2K is ascribed to a canting of antiferromagnetically coupled sublattices. Specific heat and dc susceptibility measurements show that (H₃O)V₃(SO₄)₂(OH)₆ undergoes a sharp antiferromagnetic transition at 21K to an ordered ground state. However, neutron diffraction data taken at 4.2K reveals no evidence for long-range magnetic order. It is suggested that the magnetic ground state could be a highly correlated spin fluid.