Hyacinths dying

Hello, I'm a bit of a newbie and I was just wondering why my hyacinths are dying? My pH and nitrate levels are normal, my koi are healthy, and there are no algae in my pond. Also, what's interesting is that I have a bunch of oxygenator plants and they're growing faster and healthier than my hyacinths (well that's because my hyacinths are doing the opposite of my oxygentor). Anyways, what could possibly be the problem and do I need to pour some of that plant fertilizer to make them grow, because I don't :P.

Thanks.

I kept having this problem last year also, but the koi were eating all the roots off of them, causing them to die. I didn't buy any this year... I think next year I'm gonna make a section of the pond blocked off so the koi can't eat everything.

I live in a lower sub tropical climate. Every winter the water hyacinths die back. Do you live in a colder climate? Otherwise them might not be getting the nutrients they need if there are no fish or just a few.

Hyacinths do not tolerate high pH (9) or salt levels (>.20). You didn't say was your actual pH result was.