tcook1
Here's what I do to make SURE my guys have access to calcium at all times.
I have 4 sources of calcium in the cage at all times.
1) a cuttlebone
2) a mineral block - you have to knock the corners off and rough it up a bit, otherwise its too hard for their bills
3) a treat cup full of the blue ABBA Mineral Mix (which you need anyway, or something like it)
4) a treat cup full of crushed egg shells.
They need to have this in their cage freely available 24/7. Its not something you just give them once in awhile. They may ignore one or several of these at any given time but DO NOT remove them (except to dispose if they get dirty/pooped on). They will be there when they are needed. My guys totally ignored their crushed egg shell for over a year then suddenly gobbled it down. So don't just decide they're not and will never use a particular source because when they need it, they need it right then.
In addition, in order to make sure they can utilize their calcium, I use Oasis VitaDrops in their water. Again, this is something they need access to all the time. The VitaDrops have vitamin D3, which is needed to process calcium (among other things). Finches normally make their own D3, but that requires lots of natural sunlight which caged birds inside a house do not get enough of even if they are sitting right in a window - because window glass is made to filter out the specific wavelengths birds need to make the D3.
There are artificial lights that purport to facilitate this process in place of sunlight but they are of dubious utility. For one thing, the bulbs stop producing different wavelengths of light as they age and there is no way, without lab test equipment, to know if the bulbs are still "good" for this or not because its not visible to the human eye. Plus other reasons. So I do NOT rely on artificial lighting for this either.
Any vitamin mix that has D3 in it would be fine, doesn't have to be Oasis. However it should be a vitamin supplement that goes in the water and not dry powder you sprinkle over their food. The "sprinkle on their food" type of vitamin cannot be calibrated - eg you can't ever be sure that just because you sprinkled it on some seed or even mixed it in a mash just how much the birds are getting.
However "thirst" is pretty well understood so when you mix it in their water, sure, the daily intake will vary a bit, but you can be confident that overall they are getting enough and not too much.
In addition, I use only silos for water - the tube thingies - because that way they won't try to take a bath in their drinking water, it keeps it cleaner, they are less likely to splash it out, and it takes up less space inside the cage. My guys will still splash it out if I forget to give them a bath at least 2 or 3 times a week.
Slip a kid-size sock over the tube if you experience problems with algae growth but I've never seen that myself. Covering the tube with a sock will keep the light out and put an end to that problem if it occurs. It does make it harder to monitor the water level though so you'll have to make sure you remember to pull the sock up every day and check the level, or get some of the tinted silos that purport to block out the light that would make the algae grow. The water silos I like don't come in a tint, but that's ok for me since I have never had an algae problem.
There is nothing wrong with doing what you suggest, but it is not sufficient by itself.
I don't make egg food - with only the 2 finches its much more convenient for me to buy the Cece commercial dry egg food - but I do save shells from baking or making breakfast. I rinse immediately, microwave (only for a couple minutes but I would guess that depends on the strength of your microwave), and crush with the back of a spoon like you would for your human child should you need to give him/her a pill.
There is a recent post somewhere (can't remember where but I just read it yesterday) about different ways to easily crush egg shells for your birds.
You could also buy HATCHED! commercial crushed egg shell but IMO this product is stupidly expensive when you can crush a few egg shells up for free. YMMV, I'm on a fixed income.
Another potential source of calcium is oyster shell for chickens (available at any feed store). Comes in 25 lb to 50 lb bags but is super duper cheap in those quantities. I feed it to wild birds so its well worth it to me. You can occasionally find it packaged in much smaller amounts (but a lot more money per lb). This product must be further crushed for use by small birds, I do that with a small coffee grinder dedicated unto the purpose.
Note that the ABBA Mineral Mix is mostly crushed oyster shell already.
HOWEVER. Even having the ABBA Mineral Mix in the cage at all times is not sufficient, because there are times when your birds will need extra calcium. If their only source of calcium is the mineral mix, they will have to ingest more of EVERYTHING in the mix and not just calcium, which could cause other problems.
So place a cuttlebone and a (edges broken off roughed up) mineral block such that they won't poop on them and leave them in the cage at all times, even if it looks like they're not using them, for emergency calcium and beak conditioning. Just make sure they stay clean. EG don't place them under a perch or so close to a perch they might turn around and poop on it. I elevate my mineral block above tail-feather height by resting it on top of a finger cup.
AND have at least one source of crushed (not powdered) calcium in the cage such as crushed oyster shell or crushed egg shells in a treat cup that you keep filled ALL THE TIME, in addition to the ABBA Mineral Mix.
You could try to crush up some cuttlebone but it is so fragile it tends to powder.
The ABBA Mineral Mix is the only one I will recommend, both for its composition and because I feel comfortable with the size of the particles in it. It is a blue mineral mix, but there are other mineral mixes which are also blue and at least one of them that I have examined personally had much larger chunks than I would be comfortable with. Too large a piece of something like oyster shell could cause problems for your birds.
I'm sure there are other mineral mixes which are equally appropriate and safe as the ABBA, but I don't know what they are and I can't remember specifically which blue mineral mix it was that looked unsafe, so I stick with the ABBA.
About powdered supplements - I know some people use them but my guys very very obviously prefer supplements in large enough chunks that they can easily pick it up and manipulate whatever it is. So I use the Cece commercial egg food because it is crumble sized particles, instead of the Quicko which is more powdered, for instance. There is powdered cuttlebone out there which would be good to mix into, say, home made egg food but perhaps not so suitable to just put in a treat cup.
So when crushing your egg or oyster shells you want fairly small pieces but not actual powder.
In order to keep the cage, supplements/food, and environs cleaner, I use only tube feeders, silos for water, and finger or thumb cups and egg biscuit cups (these are shallow, narrow feeders).
Reasons:
1) too small to lay eggs in
2) easy to place so they don't poop in them
3) too small for them to perch on the cup itself, turn around, and poop in them
4) too shallow to build up a top cover of hulls that buries the seed - no need to EVER blow off the hulls or mistake hulls for seed.
I put their staple seed in a silo/tube feeder, I use a silo for water, and everything else goes in the thumb/finger cups or an egg-biscuit cup. NOT AN EGG CUP that is shaped like an egg, but the egg-BISCUIT cups.
You can find examples of these (and the ABBA Mineral Mix, also the HATCHED!) on the Glam Gouldians site. She is my go-to for things birdy.