Something like rooster booster or anything that can dissolve in water should work. Keep track of how long the water is sitting there also. Don't let the water go stale.
Look up the vitamin ratio for rooster booster and see if any of yours comes close to there ratio, it doesn't need to be exact match but close. If it does come close, use it.
Keep up with regular cleaning of where your Seramas are living in. Keep there bedding clean as possible, so it doesn't create a habitat for virus and bacteria to grow. Check them for mites once in a while during routine checkup. And are they staying inside your home?