My Pearl gourami is sitting at the bottom of the tank?

[Essjay]

Signs include white stringy poop, which indicates round worms, or flat worms or a protozoan infection.
Treatments in the UK:
Round worms - eHSa ndx (levamisole)
Flat worms - eSHa gdex (praziquantel)
Both round and flat worms -NT Labs Anti Fluke & Wormer (liquid, flubendazole) or Wormer Plus (powder, flubendazole)

Unfortunalely the treatment for protozoan infections, metronidazole, is only available on prescription in the UK.