Tube worming used to be done as a matter of coarse once a year.
The only way to tell if your current worming program is working is by having your vet do a fecal count.
However, Most horses today stay fairly worm free- Remember horses are never 100% clear as they are ground eaters, this is where everyone poops.
There are many options when considering wormers. Interval dewormers[pastes] are used throughout the year[frequency depends on variables,average 8 weeks]
Daily dewormers are found in the form of feed through supplements[pellets,powders] and will help prevent re-infestation . You must first worm with a paste or tube wormer that contains Praziquantel & Ivermectin.
The 5 most common ingredients found in wormers are Ivermectin,Pyrantel Pamoate, Fenbendazole, Oxibendazole, and Praziquantel. A rotational deworming schedule means that you medicate 6 times a year, rotating different ingredients[brand name not important] in an effort to eliminate as many worms/larvae from different species as possible.