I have my 2 quarter sized angelfish babies in a 10 gallon tank. They are fine now...but in a month or so I will be putting them into a 20 (or 29) gallon tank. If I get a 29 gallon, I might even get another angelfish (for a total of 3).
From what I've read, you should buy 6 angelfish babies in order to have good odds at finding a pair. You might have a pair with your 4, though...you never know. I don't think my 2 are a pair...they
do however swim along side each other sometimes, but I notice that my female (I think she's female) nips at my male whenever she feels inspired. Honestly, I think my male likes the female, but she only tolerates him for as long as she can. Anyways...
I said all that to say...I have no idea how big your tank is in gallons, but, I
think you may be able to keep a few babies in your tank for at least a month or two or three. But, if the tank is under 20 gallons, you should upgrade (to a 20) to keep a pair. I will say, though, that I've read on several angelfish websites that many folks keep one
pair in ten gallons...with no problems. But, I'm sure that is with very regular cleanings and with NO substrate. But, I don't want to risk cramping my angelbabies, so I'm most defenitely going to upgrade very soon....plus, I can't go barebottom because I like decorations to much.
...the general rule you may hear a lot is
one angelfish per 10 gallons of tank. Again, if you
only have 10 gallons, I think you should go barebottom when keeping an adult angelfish...with hopes of upgrading. JMHO!
I don't know how long it takes angelfish to pair off. I hope this helps.