I am generalizing, so please do not take my next statement and apply it to every triathlete you meet. Tri-Athletes tend to swim with tight/tense strokes. It is kind of like the I will just try harder to go faster philosophy. News Flash, triathletes are some of the hardest workers on the planet, so why are they not the best swimmers?
Let the hate mail come, but I am trying to help. Help everyone come to the realization that working harder at the wrong thing, will not really do anything for you except burn some calories (which isn't bad).
The issue comes down to relaxation and being comfortable in the water. The key to swimming in water is flowing with the water and knowing when to use you body for power and when to relax and glide. Maximizing efficiency is what we should be striving for; especially when your swim is 1.2 or 2.4 miles!
Ok we have established we need to relax, how do we do this?
Staying relaxed will keep you safer in the water, it will help you be more efficient in the water, and it will not only help your swim time, but your run and bike, because you will have more energy for these portions of your race.
Go get back in the water, and don't stress about the workout, Relax.