It sounds like to me that the bacterial colony might have died. You're going to have to be patient. It takes some time for the colony to grow back. If you are in the US, you might want to try to locate some BioSpira, it is pretty much the only bacterial starter that has evidence that it works well. BioSpira is only available in the US, though, so if you don't live here, I don't know the equivalent products anywhere else.
I know it sucks doing water changes everyday, but it will come out okay in the end. The fish are much better off than if had let them swimming in the pollution.
edit:
you know, I just thought of another possible explanation. Are your other plants doing good? Growing vibrantly and good color? The reason I ask is because aquatic plants prefer to take up ammonia as their nitrogen source. And, if your plants had been taking up ammonia to grow, they may have been taking up so much as to not let the bacterial colony grow. Then, when that plant died, it left a void in the amount of ammonia that was being taken up. So, you might want to check your plants' health. If you use CO2, is that still going correctly? Have you fertilized the plants lately? etc. The solution to this may be as simple as replacing that large plant that died.
I know it sucks doing water changes everyday, but it will come out okay in the end. The fish are much better off than if had let them swimming in the pollution.
edit:
you know, I just thought of another possible explanation. Are your other plants doing good? Growing vibrantly and good color? The reason I ask is because aquatic plants prefer to take up ammonia as their nitrogen source. And, if your plants had been taking up ammonia to grow, they may have been taking up so much as to not let the bacterial colony grow. Then, when that plant died, it left a void in the amount of ammonia that was being taken up. So, you might want to check your plants' health. If you use CO2, is that still going correctly? Have you fertilized the plants lately? etc. The solution to this may be as simple as replacing that large plant that died.