I have a blackstar ht-5r combo amp..... Would I get a clearer sound using the effects loop with my distortion effects pedal compared to plugging pedal into front amp input then using clean channel? Would it still be a heavy big tone through effects loop?
Short answer: Certain effects like overdrives and distortions typically go in front of the amp. Other effects like reverbs and delay typically go in the effects loop (when possible).
Long answer: The effects loop on an amp usually sits between the pre-amp and power amp sections. Most of the "tone" of your amp comes from the pre-amp. Pre-amps tend to enhance the effect of (and will be enhanced by) overdrives and distortions. However they also tend to diminish the effect of delay and modulation style effects.
The power amp section pretty much makes the signal louder, so delays and mod effects remain clear when put right before the power amp, but overdrives or distortions would likely sound harsh and unappealing without being smoothed out by the pre-amp.
It's a bit of a generalization, but it works most of the time.
The conventional usage is to put distortion effect in front of the pre-amp; then, when you engage it, it drives the pre-amp harder, so that you get both the pedal's intrinsic distortion as well as pre-amp distortion.
That being said, you should try both positions, and see what you like; there are no hard and fast rules.