If your Gouldians are in an outside aviary environment like mine and are exposed to wild birds, insects, snails, and slugs, you should seriously consider worming them.
I learnt the hard way by not worming my colony over the years. I have no doubt this was the very reason why I continually had adult deaths at various times throughout the year. I now worm my colony every three months and I no longer experience adult deaths as I did in the past!
It is a good idea to vary the Brand of worming medication from year to year or as it runs out. I am currently using an Australian product called, Worm Rid, by Avian Science. Active Constituents are 10mg/mL Levamisole Hydrochloride equivalent to 8.48mg/mL Levamisole base plus 2mg/mL Praziquantel.
It is a broad-spectrum that kills Thread Worm, Caecal Worm, Round Worm, Gape Worm, Gizzard Worm and Tape Worm. Treatment is via their water for a 24-hour period and then they are treated again in 14 days’ time.
There are many broad spectrum worming medications around so just take your pick.