I have not used chatted seed. I just grow my own grass seeds. It's really easy. 30cm plastic pot with some shade cloth in the bottom to stop potting mix draining out the holes. Fill pot to about 1 inch below top with basic potting mix. Sprinkle a handful of finch seed over the potting mix. Cover with a thin layer of potting mix and then water. As soon as the seed sprouts and you see green grass, start fertilising them with Thrive liquid plant fertiliser. Use half strength and water it on them once a week. The rest of the time just use water. Start a couple of new pots each week and you can have green grass seeds all year round. When the grass seeds are lush and there are lots of them, put the pot in the aviary and let the birds go nuts
You can feed soaked or sprouted seed too. Soak 1/2 to 1 cup of finch seed in a container of water overnight. Put into a sieve and rinse off under tap water. Then gently shake most of the excess water off and put the seed into a zip lock bag. Inflate the bag and keep in a dark place for 24 hours. Take seed out of bag and rinse well under tap water, then put in a bowl for the birds.
In cooler weather the seed might take longer to germinate so just look for a little tiny root coming out of the seed. Feed it when you see the root.
Soaked seed has no root yet, sprouted seed has the root. You can feed either, however I prefer sprouted.
Replace soaked/ sprouted seed each day. If there is any left over from the previous day, throw it on the floor of the aviary and put a thin layer of sand on it. It will grow and the birds can eat the grass.
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If the birds are currently living in the same aviary and they show no aggression to each other in the aviary, they should be fine together in a smaller holding cage. If you plan on showing 3 males then they should be fine at your house in a smaller cage. If you have 2 males and 1 female then it might be safer to have the males separate from the female so they don't argue over her. The only time you don't do this is if you have a bonded pr, then they stay together in a cage. Or if you have a family, the family stays together. But it sounds like you are just going to show 3 young males and they should be fine together.
Keep the 3 together (assuming they don't fight) until the night before or the morning of the show, then put them in their individual show cages.
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Yes, quarantine your show birds separate from any new birds you get at the show. And try to keep them in different parts of the car travelling home. I know it sounds obsessive but you have to treat every new bird as a potential disease bag and the less contact they have with your birds, generally the better. So keep them on different sides of the car if you can. When you get them home have them in different rooms and when you feed the birds, do your aviary birds first, then your show birds, then the new birds last. And wash up with warm soapy water after feeding/cleaning them.
If your show birds are fine and healthy after a week, and the new birds have shown no signs of disease, then put your show birds back in the aviary and continue quarantining the new birds for a few more weeks. If any of the new birds show signs of disease during the first week, keep your show birds quarantined for longer too. Birds have to show no signs of disease for at least 3 weeks before I add them to an aviary.
While in quarantine you can treat all new birds with Ivermectin or something similar to get rid of any parasites like air sac mites, worms, etc. You can listen to the new birds breathing and if you hear them gasping or making any funny noises while sitting there resting, then they probably have air sac mites and will need treating. If any of the new birds have air sac mites, then treat them and the birds that went to the show.
Be careful about feeding green feed to any new birds. Try to find out if their owner fed them greens on a daily basis. If the birds were not fed greens every day, then only offer a very small amount of green feed to the new birds each day. Too much green food given to birds that don't normally get it can cause an upset intestine and make them sick. Same deal with soaked/ sprouted seed or any new food. If the birds have not eaten them before, then only offer a small amount every couple of days so the birds don't gorge themselves on new food and become unwell from a sudden change in diet. Gradually increase the amount of greens and how often they are fed slowly over a few weeks.