The evil unstoppable Granatoid Tanks everyone is so afraid of are defeated by an elderly pensioner.

With some jewels around her neck which can affect the Granatoids.
I can't remember what the jewels are called, I'll have to watch the episode again.

They are Plyton

But they're supposed to be practically invincible, the Cybermen of Fireball XL5, and they run away from a pensioner!

Yes, Cybermen and Granatoids have a lot in common, for example Cybermen are afraid of Gold and Granatoids are afraid of Plyton.

When XL5 lands and the crew disembark, Steve tells Robert to 'keep on free float'. I assumed that could only be done in space.

When Zero calls an alert over the mall intercom, we see a shot of Ma Doughty's shop and her in the shop front, but in the next shot she's in the back room with Matt and Steve they were playing the disc.

Aw. Matt and Steve are so happy to get Venus that disc.... bit of a bummer cos she already has the thing! She plays it in The Doomed Planet.

Could be the single

Professor Matic seems to be a pretty handy musician! I enjoyed listening to him play.

Why do they choose such ugly planets to colonize? What could they do with soil that is made of glass? Wouldn't it be like living on an old lava flow? There didn't seem to be any plants at all.

Given that they had an emergency mission, would they really bother with loading a musical console on board? Especially since it ended up in the Command Center of Space City?

Steve couldn't seem to make up his mind about the mission. First it seemed that they were to rescue the mineralologists and their equipment, then he decided that they had to stop the Granatoids. Why not get the civilians safely away, and then come back and try dealing with them?

They are aware that the mineral Plyton will repel the Granatoids. Ma Doughty happens to have an unusual necklace of stones, given to her by her father, who had dealings with the Granatoids in the past. He told her that with that necklace, she could never be harmed by Granatoids. Say, you don't suppose....

BTW, I don't think much of the Professor's Plyton detector. Apparently you have to be right on top of the stuff before it will sound off.

Why would they want to have Venus' party in the Command Center, anyway? Commander Zero would have been well within his rights to boot them all out of there. What if an emergency had come up and they missed it because of the loud music?