Hi and welcome to the forum
What are the tank dimensions (length x width x height)?
Which part of WA are you in?
Perth normally has very soft water due to the desalination units that provide us with drinking water. Some of the country towns might be different.
Mollies want a GH above 250ppm and a pH above 7.0.
Platies should be fine at a GH of 180ppm.
Most tetras should be fine at 180ppm too as should the cichlids.
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Don't have 2 species of dwarf cichlid in the tank unless it's over 4 foot long because the Kribensis will bash the rams when breeding. If you want a breeding pair of rams, buy 8-10 young fish and grow them up together. Let them pair off naturally and move the prs into their own tank or move the others out and leave the pr behind.
To get a pr of Kribensis, buy a male and female or see if 2 have paired up in the shop. There are other species of Pelvicachromis cichlids like Kribensis but less common and more colourful. Pelvicachromis subocellatus from Moanda is a beautiful fish but you might have to get the shop to order them in for you.
Apistogramma cacatuoides is a nice dwarf cichlid.
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Avoid dwarf gouramis (Colisa lalius) and all their colour forms. They regularly have Fish Tuberculosis (TB) and or the Gourami Iridovirus. The Iridovirus is not meant to be in Australia due to the 4 week quarantine period but it still appears from time to time. Neither disease can be treated and once the disease is in your tank, it's there until you disinfect everything, including the fish.
There are other small species of gourami that don't normally have these diseases.
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The following 2 links are for 2 of the major fish suppliers in Australia. They don't sell to the public but they do supply most shops. You can see if the fish you want are available from the suppliers and then ask the shop for a price and to order them in for you.
Listing of LIVE FISH products
www.premierpet.com.au
Each week, Aquarium Industries posts a list of the stock that we currently have available for order on our website as a downloadable excel file.
www.aquariumindustries.com.au