Sorry mate i completley missed this i went away must have missed it when i came back sorry again
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As with tropical tanks the bigger the better, how ever small isnt impossible. You just have to keep a close eye on things, as the smaller the tank is the quicker things change.
With marnie tanks you can use various forms of live to keep the substrate clean hermit cras are just one example. Water changes are slightly more complicated than a tropical tank for the obvious reason you need to mix it to the correct salinity first which means you need a heater air pump or power head and a big enough container to store it in while you do the mixing. To get the water out i just use a long hose straight out into the garden.
The main thing with saltwater tanks is keeping the water quality good, do you know what kind of tank you want? Do you want to keep corals or just fish for example.
Hope thats of some help my apologiese again if you have any more questions just ask and i will answer them a bit quicker next time
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