Clown Loaches are very susceptible to ich, (white spot), it is more than likely the situation you are facing but this cannot be confirmed without photo graphs. Ich is a parasite, a small worm like creature that exists in the water and will burrow into the flesh of stressed out fish. this parasite can be fatal to fish especially to Clown Loaches as they have very soft skin, with none or hardly any scales to protect them. Most advice out there is to medicate with White spot cure. Be warned from research that ive done about this medication is that it is actually cancerogenic (cancer causing) in America items containing this ingredient has to have strict warnings on them. My advice is stay the hell away from it, it can kill you, is that something that you want to be putting it into your fish tank? imo. i have had ich on Clown Loaches and to begin with suffered fish losses. But from my understanding of the parasite i now have some effective strategies for dealing to this nasty little beast.
1. Raise the temperature of your tank to no less than 28 degrees no higher than 31, this is also the optimum temperature for your loaches, i would suggest if your tank is not at this temperature then it may be one of the causes of your fish becoming susceptible to the parasite. But most importantly raising the the temperature speeds up the life cycle of the parasite.
2. The white spot on your fish is a cyst, only a symptom of the parasite, this is where a parasite has burrowed in and is feeding off the host fish. Once this parasite has burrowed into the fish it will multiply and then leave the host fish to find other likely victims. Which is another reason why clown loaches are so susceptible. The parasite will fall to the gravel in your tank where Clowns spend most of their time.
3. Do 10% daily water changes, this is to focus purely on syphoning the parasite out of your substrate to reduce its numbers.
As long as your fish are eating and active, they are in no real trouble, so what ever you do don't overreact.
Nail the parasite, keep the fish happy, make sure that you are dong everything you can to provide the best possible set up for your Clowns (fast flowing clean water, 28 to 31 degrees not colder check that the tank temperature is not dropping during these clod winter nights).
Don't use salt as Clowns don't like it.
The white spots may last 4 maybe 5 days don't worry the parasite will only spend 12 hours in the fish, this can be shortened by following the steps outlined above.
Clown Fish are cute but require very specific factors to keep them happy meet these requirements and no problem. If you neglect them, well you are going to have trouble. They are some of the best fresh water fish to keep and there are websites devoted to them, do your research it will reward you with beautiful happy fish.
Remember the parasite is in your tank although you have removed the infected fish you have done nothing to battle with the parasite. Netting the fish may have had the negative impact of placing already sick fish under more stress. All the best with your Clowns.