Okay, that’s good to know. Since you are not having a problem with ich in your seahorse tank, and you merely treated it with copper before the seahorses arrived as a precaution to make sure it was ich free, then I would definitely leave your pregnant male and his mate in your main tank and allow him to give birth there. That’s a much better idea for all the reasons we have been discussing in your other thread. It will be much less stressful on your pregnant male to remain amidst the familiar surroundings in your main tank with good filtration, lots of hitching posts and shelter, the company of his tankmates, and most importantly of all — a fully functional biofilter — than it would be to transfer him into a bare nursery tank that’s only 2-5 gallons with just a sponge filter that has not cycled yet.
Seahorses tolerate copper sulfate in therapeutic doses very well, so the copper in the main tank is not a problem. Even delicate seahorse fry can tolerate exposure to copper at the usual treatment levels, but you won’t want to fill the nursery tank with the copper water from your seahorse tank since there’s no sense subjecting the newborns to harsh chemicals unnecessarily. So fill your nursery tank with freshly mixed saltwater and adjust it to the same temperature, pH, and specific gravity as your seahorse tank while you are waiting for your male to give birth in the main tank. The newborns can then be transferred directly from the main tank they were born in to the nursery tank with no acclimation whatsoever.
Just be very careful when transferring the babies into your nursery tank and they will be fine. NEVER lift the newborns out the water when transferring them. They will swallow air and develop fatal buoyancy problems that leave them bobbing helplessly at the surface, unable to submerge or eat (Giwojna, Jan. 1997). Netting them out or otherwise exposing the newborns to the air is one of the most common mistakes inexperienced breeders make, and it often results in the loss of the entire brood (Giwojna, Jan. 1997). The proper way to move the babies is to carefully scoop them up in a small cup or bowl, and gently immerse the cup in the nursery tank to release the fry (Giwojna, Jan. 1997). Or a common turkey baster works well for gently sucking up one or two of the fry at a time along with a little water, and then releasing them into their nursery (Giwojna, Jan. 1997).
Best of luck with your pregnant Zulu and the upcoming fry you are expecting, Nigel!