Is the bulb still attached? What are you using the hyacinth for? If you are just using it for a vase arrangement then I would put it in water they last a very long time. When you bought them were all the buds tight? They will grow if the bulb is left on and they are in water.

Yes, bulb is still attached.

What do you recommend ? I usually put floralife and water and with the weekly or 2 week long flower cuts, I change them every monday.

With the hyacinth, I was looking at the growers site and they recommend every 2 days.

I just asked my daughter who works at a florist shop and she says they leave the bulb on for arrangements unless, they think the customber might not like it. They use plain water (for just hyanciths) of course, if you use them in a mixed arrangement you probably want to use floral preserve, the more you change the water the longer they'll last so that's up to you. The hyacinths I've seen that come from market are pulled in very tight bud stage with the bulbs clean and cut so it looks square.
Hope this helps, my hyacinths are now just ready to pick.
Kathy