how intense tempo

How intense can tempo be. For example, last night i did 4x4x50m with 30sec rest and 90 between sets. It was aerobically taxing, but i just felt very minor fatigue in my legs and i think it was more from my lifting the day before, legs were pretty sore. Is this okay for a tempo workout.

I think the problem (if there is any) is the lack of rest and length of intervals — you need more rest to avoid fatigue (remember tempo is ‘active recovery’) and longer distances as recommended by CFTS; distances of 100-400m

How fast were these runs?

I’d go with doing a variation of distances ranging from 100-400.
So you can start off with 300s and start going downwards to maintain a specific intensity. Or if you are good enough you could start low and go up. Be creative