Bloody white spot!

Hey all,

as I'd expected, my continuing foray into goldfish keeping is still proving
to be a learning curve - I didn't realise that as well as my Tetratest
strips (which test for KH, pH, NO3 and NO2 levels), I needed an ammonia test
kit too... my goldfish was getting poisoned by the ammonia and did NOT look
happy, and had contracted whitespot on his tail.

So I changed 50% of the water, and started dosing him with white spot
treatment... this has certainly helped, but I have a couple of questions:

1) How long does it usually take a goldfish to recover and how long should I
be giving him the treatment every 48 hours?

2) He's been hiding all day, only emerging to get food, and I'm not sure
whether this is a side-effect of the medication or not. His movements
certainly aren't as violent as before, he doesn't look stressed, but I'm
always worried when I don't see him for most of the day. Could this be
related to my KH problem? Other water tests are fine: nitrite at 0, nitrate
at 25 mg/l, GH at 12 degrees, pH at 7.... but KH is still arouind 1 degree.

3) I'm thinking of putting a heater in to stabilise the temperature as my
room often gets quite warm them quite cold: I'm also thinking of putting
tropical fish in too (it's only 21 litres so probably tetras and / or a
zebra)... I assume the goldfish will be more than happy in warmer water?

4) Could it be that the fish is just lonely? He's in there on his own...

And to think that I thought goldfish keeping would be easy! 2 golds and 4
fantails dead already, and I'm damned if I'm adding to that total this time!

best

R