4 is way too many for a 10g tank. They need 3-5 gallons per DP, 5 being best! I have 1 DP in my 10g and its fine. Plus, lfs's sell DP's young, so you can't sex them. If you got two, and they were male and female, you'd have complete and utter chaos in that tank. 1m:3f. Stick with 1 to two tops in your 10 gallon. With how aggressive they can be, you dont want dead DP's!