Gosh, this is a great thread. You are asking lots of great fry questions. Here's my two cents.
I have tried breeders only to have the female become obviously stressed. One died. Now, if I really want the whole brood, I move the female to her own 5g way before she is due. Then remove her when she drops them. Otherwise, drop a bunch of floating hornwort plants(plastic is fine) in your tank. The fry love to hover in them along the surface. You can skip the whole pipet thing by feeding your adults a few flakes to distract them every time you feed First Bites to the fry. Put the First Bites over the floating plants. The ones hiding there will eat it. The hiding ones will catch on. For their first week or so, leave the lights off unless its time to feed them. You'll be amazed at how fast they come up to eat whenever you turn on the lights. This will help your algae issue too.
Sexing platies is not posible until they are too big for them all to be in your 15g. And I have read there is some evidence that livebearer females can keep sperm alive for fertilization for their entire life! Amazing. They think the sperm live off of some special sugar produced by the ovaries. Go figure. Anyway, once your fry get big enough to crowd your tank, have a craiglist giveaway and keep the cutest ones for yourself. If some of them turn out to be male once they get big enough to tell, give them away too. You will be able to sex them by the time they are mature enough to mate. Just don't expect the babies to stop from your 2 perma-pregnant girls. Be attentive to your fry and get rid of those males. You will get some virgin females that can stay that way.
As the owner of livebearers, you have to get a method of keeping the fry from overloading your tank no matter how big it is. My 75g is maxing out as we speak. So, don't get too concerned with saving every one. They aren't all meant to survive. That sounds cold, but you really cannot afford to get out of control in a 15g or your original fish will suffer. That said, I LOVE my babies and can watch them for hours and hours. I know what a special experience raising fry is. I'm glad you're enjoying it. I have well over a hundred fry right now. Somehow, I even have two of the cutest baby cory cats! LOVE their teeny weeny little whiskers! Those little guys will both stay, but the majority of the others will find new homes. The reality that you cannot keep them all is a sad thing
Regarding your algae- this is a natural issue with fry in the tank because they need alot of food. First off, realize that a bit of algae in an unplanted tank is not a horrible thing. The fry will graze on it and its quite natural to have a bit. Keep it cleaned off the glass and scrub your plants now and then to keep things pretty. Whenever you have fry, you will have to do weekly or twice a week water changes. This will control the algae and keep the water clean for your fish. Skip the chemicals. Its cheaper and better to change your water. After the fry are a few days old, they catch on to keeping away from the gravel vac. You can siphon from the top, but your gravel needs frequent cleaning with frequent feedings. If you siphon into a bucket, just check for fry and net them back to the tank if you get some. Your filter presents a bigger problem. I have found that panty hose over the intake gets clogged up. I cut the netting off a net and put it over the intake with a rubber band. You must use filter media, so covering the intake somehow really is your only option for the filter issue. It works well. Personally, I would skip an algae eater because you have a pretty small tank and that's one less platy you can have due to your bioload.
Sounds like you're getting the hang of the whole baby thing. Keep up the good work!
