Anything between .25-.5 means a water change. Anything over .5 is BAD. There's many diseases that can pop up... bacterial infection, ammonia poisoning, pop eye, fin rot, etc.
Basically, do a 100% waterchange NOW. anything above 1.0 is toxic. As in dead fish. So here's a chart (I thought it up, so I might be wrong)
.25-.5 waterchange (100% uncycled, 10-25% cycled) a bit too high and you'll get slightly lethargic Bettas
.5-1 Doing bad. 100% (Or 50% for cycled tank) waterchange.
1-2 Very bad. The water is turning toxic, and there's a risk of disease.
2-3 Terrible. Deadly. Diseases, too.
4+ You're fish is dead. within 24 hours....