Monitoring poops will never tell you for sure whether or not your birds have worms unless you see them. Not seeing them doesn't mean they're not there. It's the nature of worms to stay inside the body (where they won't die) and just send their eggs (microscopic - don't try looking for them) out in the droppings to infect other birds.
So it's a good practice to worm either on the results of a "fecal egg count" done by a vet (they look under a microscope for the eggs, not for worms) or to do a preventative worming twice a year.
I aim for when my birds aren't laying, preferably before they molt.
Also aim for natural prevention methods in between. That means very dry porous dirt. In other words, course sand controls worm infestations better than top soil or heavy dirt. Dry is better than moist. Compacted horse-stall shavings are more dry and better against worm infestations than hay. You can try using things like VermX, cayenne pepper, or DE (food grade only, very sparingly) in their feed in between wormings in hopes that they help keep numbers lower. I don't believe any of those products actually treat an infestation.
If you worm twice a year, worm the first time with Wazine. I wait til 4 months but my babies aren't on dirt til that time. If yours are, you can work as early as 8 weeks with Wazine. But I'd wait til later unless you have a reason to believe they're wormy. Then first worming, do wazine first - then follow up in 2-4 weeks with a stronger broad-spectrum wormer like fenbendazole, Valbazen (albendazole), or ivermectin. Wazine doesn't kill larva of rounds, but the latter products do. So you won't have to keep repeating the worming.
Some people recommend worming more often, I like to worm less often, work on the environment for worm control, and use a broad spectrum that twice a year after the initial wazine treatment.
As for the droppings, when you see loose droppings, try providing more living bacteria to help assist the gut in the form of yogurt, acidophilis capsule/tablet contents, or Probios brand dispersible powder. Beneficial bacteria line the intestines and naturally help the birds be more resistant to diarrhea and illness. (They also provide B vitamins and help the birds digest their food more efficiently.) So giving this in small amounts helps when you see diarrhea.
