You might check with local shops (chemists or veterinary or livestock) if anyone has
- formalin - extremely effective against white spot
(when used in combination with malachite green, there is synergy of action, so one of most effective external parasite remedies, but has potentially more side effects than formalin alone)
- metronidazole - not ideal for whitespot but decent if it's not an "infestation"
Note that neither (& most) medications should be combined with heat re lowered oxygen levels (& other possibles)
The 30C is quite hard on plants, it is also rather hard on fish that are already struggling to breathe (ich parasites generally lodge in gill structure before being observed externally).
Note that if ich spots are large & raised, this is a very aggressive strain (ich parasite can complete life cycle on fish which leads to the amorphous spreading spots) & should not be treated with heat.
When doing the heat treatment, water changes should be done every 12 - 24 hours with thorough vacuuming of substrate to remove ich lifecycle stages