I agree, with that lighting only a BTA would do well, thankfully Clarkii's love them. I just moved my new tank bred pair out of quarantine last night and they took right to the BTA within 10 minutes (you can see them in my gallery). A Clarkii at 3" has most likely already turned female. I would get a small juvenile, not much larger than 1" so that you can be pretty certain it hasn't sexed up yet. That would certainly improve your chances of them pairing off.
The larger female will test it and the smaller should twitch like it has siezures to show that it is submissive. When the larger accepts the smaller as a mate she will often twitch back in response. If she doesn't it is nothing to worry about, just make certain she doesn't do any damage. If you see the smaller one hiding up in a top corner near the water surface and not leaving that position then you may have to remove it, it is likely extremely scared.