I think there's a decent chance you should be worried, but not for the reason you think. That looks like 6+ inches of substrate. With that depth you can easily build up anaerobic pockets that can harm your fauna. Unless you do regular substrate maintenance you run the risk of killing your critters. As far as that algae goes, it looks to me like cyanobacteria. As far as being worried, you'll have to do some more research and/or wait for some of the other guys here to chime in and see what they think.