The heat should deal with the white spot. If 30C isn't working, you can try 31C or use a chemical based medication that contains Malachite Green.
Don't use heat and medication tho, just use one or the other.
Malachite green is carcinogenic (causes cancer) so avoid getting it on your skin and wash hands with soapy water after handling any medication or working in the tank.
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Before you use medications, do the following.
Work out the volume of water in the tank:
measure length x width x height in cm.
divide by 1000.
= volume in litres.
When you measure the height, measure from the top of the substrate to the top of the water level.
If you have big rocks or driftwood in the tank, remove these before measuring the height of the water level so you get a more accurate water volume.
You can use a permanent marker to draw a line on the tank at the water level and put down how many litres are in the tank at that level.
There is a calculator/ converter in the "FishForum.net Calculator" under "Useful Links" at the bottom of this page that will let you convert litres to gallons if you need it.
Remove carbon from the filter before treating with chemicals or it will adsorb the medication and stop it working. You do not need to remove the carbon if you use salt.
Do a big (75-90%) water change and gravel clean the substrate. This will remove a lot of the parasites and buy the fish some time.
Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn.
Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.