Sometimes it depends upon the "personality" of the guppies as to how aggressive or how inclined to courting they are. Higher temperatures (towards 80 degrees F/ 27 C) also make for more movement and even aggression among guppies and some other fishes. Excellent water quality and good feeding (which sort of work against each other) also may make them "better mannered."

You didn't mention what size of aquarium you have. Lacking information to the contrary, let us assume that it is a 10-gallon tank. I do really applaud the fact that you didn't put more fish in initially. Actually half of them, maybe the reverse trio (m-m-f) of guppies might have been best. They would have gotten your nitrogen cycle off and running.

If you have a little spare cash - then you are a remarkable person these days. ;) But another approach might be to plant that tank as heavily as possible. You need the lighting. A mere 15 watt light in the now old-fashioned tank lights might need to be on at least 12 hours a day. (Wattage + duration of hours are both very important.) And that still might not be enough to grow thriving plant.

If you lived near me (southern 'burgs of Chicago) I could invite you over and send home a bag, of the sometimes embarrassingly fast growing hornwort, full enough to completely fill your aquarium. It is not too expensive at the shops and if you get a couple of nice green pieces, with very full growing heads, they would do well on top (though DJ has pointed out that the stuff will even grow up from the gravel if one end is buried there) with a few Valisnaria planted in your 1" of gravel. (Polk the hole with a finger, gently set the plant in there and carefully slide the gravel into the hole - never force a plant into the substrate.) They could fill your aquarium in a most attractive way. For a little more on plants, go to Immediate Help (the link is to the upper right corner of this page) and check out the plant section.

See also
http://www.naturalaquariums.com/plants/ceratophyllum.html

Your platys are likely to be good companions for your guppies. Indeed, with some plant cover and well fed adults, you probably would get both fry of the platys and guppies.

Now your "Chinese Algae Eater", really from Thailand, while probably an excellent algae cleaner when under a couple of inches, will in time change its diet, become a territorial bully and maybe be better known as a "Siamese Slime sucker." And your guppies could then become victimized and even harmed fatally. Theoretically it could grow 11 inches long. It is unfortunate that your fish seller neglected to mention all of that. Will they take it in trade for some hornwort?

Even if an algae eater is consuming algae on the tank sides (and yes, young they will plow through hair algae) they are digesting the stuff and passing the nutrients (via feces & urine) right back into the aquarium where the extra ammonia and other nitrogenous wastes will encourage the growth of more algae.

A better approach to algae would be to either limit the light going into a tank or get some fast growing plants to absorb some of those nutrients in the water. Whether you have plants or not, you also should be doing partial water changes with treated, "seasoned" water of the same temperature. With your current fish load, you would be doing well to a 25% partial water change nearly every week. With more fish, you might wish to increase the percentage of water changes up to nearly 45 or 50%.

If you do not have a gravel vacuum, get a fast request off to "Santa". An important part of those partial water changes is getting a lot of that "dirt" out of the gravel and that can only really effectively be done in a graveled aquarium with one of those gizmos that draws the "mulm" out of the gravel and out into a bucket. Maybe not right now, but that waste water from an aquarium is great for watering and nourishing plants in a garden.

When I moon lit in a fish shop, I startled customers by refusing to sell them Chinese algae eaters. I would mention their tendency to become nasty bullies and suggest that more gravel vacuuming, leaving lights on less hours and cleaning the little green algae growing on the sides of a tank with one of those cheap, soap-less, plastic pot scrubbing pads would be a better way to go.

Actually a little green algae growing on the side of an aquarium is a sign of a healthy aquarium. When I was pretty new to the hobby, I heard that that algae could be removed with one of those razor blades in a little holder. It worked, but I worried a little about scratching the tank side. Because the rapidly increasing guppies (one pregnant female to 232 guppies in a year) were so ravenously enthusiastic about eating that algae as it got scrapped off, even off of the blade itself, I worried a lot more about accidentally chopping somebody up with that blade. The pot scrubber proved to be messier (though when the water settles, a lot can be siphoned from the tank bottom) but easier on me and the guppies. ;)

That population consideration is another reason why you might not want to get more female guppies. About a year and a half ago, I "guestimated" that if all the offspring survived from four females and five males, they could become over a 100,000 guppies in a year. :)

http://www.guppylog.com/story/2005/2/20/15155/6360

I can't find it right now. but a gentleman wrote in and suggested that my numbers were actually quite low. He offered higher figures. :0

So it isn't necessary to save every last fry. ;)

As a newer aquarist, you may already have considered asking for some aquarium related items for Christmas or Hanukkah. Is it out of line to give aquarium stuff as Kwanzaa gifts? I would also suggest looking at the reading list at the end of Immediate Help for useful books. A few years ago, another fishy Christmas list, was offered on Guppylog:

http://www.guppylog.com/story/2003/11/17/10939/076

It is a little late to be making such suggestions, but they may still have some usefulness.