I used a apparent expired bottle of DT's once, smelled fine..but I think it was the shipping, clouded up my tank real good but thats about it no water chemistry problems, I did a 25% water change and ran some carbon..it didn't really have a smell at all.
It has been s year since I have purchased DT's. THe LFS finally started carrying it and I purchased a bottle. It appears its has changed a little including a different bottle and a more concentrated solution. However, it has a odor that reminds me between fresh veggies and my sump... Is this normal? The less concentrated did not have any smell.
i have no experince with the old dt's but the concentrated bottle says "dead phytoplankton will have a strong foul odorand should not be used." It also has a best if used by date. i thnk it should be alright.