Question about expired fish flakes/pellets

[chevy4w]

Not sure if anyone can answer this question. I've been having quite a time with diatoms for a long while now. I have tried many things to get rid of them, process of elimination. Nothing seems to be working. I feed my fish flakes and pellets once a week. Today I discovered they both were expired by just over a year. Does anyone think this may be causing the problem??? I did throw the food out and will be buying more this weekend. I'm getting more than a little frustrated.
I know that diatoms feed off silicates in the water. I don't use tap water as I have a ro/di system and all the filters are brand new.(that was my first suspicion). Vacuumed the sand bed weekly for a while. Lately I've just been blowing the sand bed. Fed less food too.
So, any ideas?

 

[Vaiodude]

Not a big fan of flake or pellets personally. I have a regimen of LRS frozen food and either nori or new era marine grazers.

 

[eatbreakfast]

Dry food once a week won't be much of a contributing factor. What salt do you use for water changes? Many have silicates. I being one of the worst offenders in this regard.

 

[chevy4w]

I have always used Red Sea regular salt since I set the tank up 4+ years ago. Never had this situation before so unless Red Sea is doing something different I don't think it would be the salt.
Has anyone heard of any problems with Red Sea salt?