Powering up 2nd Blissey

FTM the 89% to ZH, first of all. I personally wouldn't waste RC on Blissey or anything else that isn't a Legendary (unless I'm absolutely drowning in RC) so just be patient, walk your Chansey a bunch and power it up whenever you've earned enough candy to do so.

It really isn't worth rare candy. An 1800 Blissey takes almost as much time to take down as a 3000 Blissey.

The single Blissey should get a lot of the work done. Consider other 'mons to supplement it, such as Gardevoir/Gyarados/Dragonite. These 'mons force a switch from common attackers and all have slower, stronger quick moves and access to multi-bar charged moves.

I usually only advocate for rare candies on legendaries (as other mons can be walked), but some play in areas where pokes are hard to find. Though I understand this, I would not use rare candies on something used for paltry gym coins, especially if you already have at least one great defender at your disposal.

I have 2 LVL 40 95.6 IV Blissey's and my next one is Chansey 97.8 IV. I want 40 lvl Chansey to be gym defender when you try to keep Raid gym. It is pretty hard to take gym if there is maxed Blissey and Chansey together!