Big Cramp in the pool today after a hard bike session

Went to the pool today and was swimming pretty well until I cramped right at the end of the workout.  

Warmup

Mainset

2x250 Mod

4x50 with 25drill and 25 build

2x200 Mod

4x50 with 25drill and 25 build

2x150 hard

200 kick 

200 Cooldown (free/back)

I started to do the 200 kick at the end - 50 with kickboard, then put on fins and foot cramped right up.  I decided to skip the kick and do the cool down

On my last 25, I was swimming on my back and BAM - my right calf cramped hard - huge knot in the calf - it's going to take weeks to recover from a cramp like that.  Last time I had that was in the AC half IM this summer.  

So why did this happen?

- From a 20 min FTP test on the bike trainer earlier in the day

- Limited electrolyte intake today

- Too much chocolate (caffeine over the holidays)

Who knows, but I've got to get this fixed. Might need to check out #itsthenerve supplement