If you suspect intestinal blockage/constapation, withhold all food for a few days (they'll be fine, don't worry), add 1tsp/5g MgSO4 (Epsom salts) to the tank and try feeding the fish a pea - remove the outer skin first, and if it's a frozen pea make sure it's completely thawed. Both epsom salts and peas have a laxative effect for fish, so you should see them produce a lot of waste.
What type of infection to you suspect? There's a different solution to each kind. I'd try the above, see if it helps, and if not keep investigating. Tigers are greedy little things, and dry foods can sometimes cause blockages. Fish that eat a lot of flakes before they have time to swell in the water can have problems when the food swells in their stomachs; this could be the case with your little guys.