Purigen and chemipure pretty much do the same thing, only difference is chemipure is carbon and GFO, where as purigen is a propitiatory media that does the same thing.
I don't mean to be particular, but this perked my ears (you know, those ears I listen to conversations over the internet on reefcentral forums with). I always understood Purigen to be specific to ammonia/nitrogen cycle related function, where as carbon was very much for broad-spectrum absorbtion.
I checked on Seachem's site, and they specifically state:
Purigen® controls ammonia, nitrites and nitrates by removing nitrogenous organic waste that would otherwise release these harmful compounds. Purigen’s™ impact on trace elements is minimal.
As I understand it, carbon absorbs everything available, good or otherwise, and has a pretty significant impact on trace elements.
Maybe Seachem has a specific porosity in Purigen to only absorb certain compounds? Maybe it's all marketing mumbo-jumbo? I dunno for sure, but I just wanted to clarify this, that it's advertised as specifically absorbing compounds as part of the nitrogen cycle, instead of just broad-spectrum like carbon.
Instant ocean salt while is OK for a FOWLR tank, you will want to go with reef crystals or something similiar thats specifically formulated for a reef system. Its the extra trace elements in a reef salt that you will miss in a plain salt mix. A good reef salt will get you started right without having to dose anything for a long time.
Bah. I started my tank with instant ocean, and many long-time reefers use it as their primary salt. Randy Holmes-Farley, ReefCentral's chemist-in-residence uses Instant Ocean, with added magnesium. You'd still need to adjust ReefCrystals to your specific application. The only reason to try other salts is that it seems like for whatever reason (or maybe just more people use it so you see more complaints) IO and RC precipitate calcium more often than other salts.
I believe the formula for IO and RC are almost identical, with RC having boosted alkalinity and calcium contents (and probably magnesium to hold them in suspension at higher levels). In theory, all of the salts should do the same thing and provide the same product. They all have a little "extra seasoning" here and there, but at the end of the day, you'll be fine with any of the main brands, especially early in the hobby.
The most important thing about salt with aquariums is that you're using it. 10-20% water changes bi-weekly. Everything else is debatable (and fine, yes, that's debatable too).
Since we're on the subject, I'd strongly recommend investing in a salinity refractometer to make sure you're measuring your salt levels properly (and EASILY; hydrometers are a pain, and mixing based on measurements on the bag WILL BE WRONG). You should be able to find one used for $20-$40, or new for $40-$100 (I don't think I've spent more than $45 on a refractometer, and they last a very long time).
