Shelf-life:

ALL Purina Fish products - AquaMax, GameFish Chow, Mazuri products made for Zoos and Aquariums - are made with L-ascorbyl-2-polyphospate. Roche's tradename for this was "Stay-C".
After one year, 85% of what we put in the mixer is still in the diet. In the old days - 50 to 75% of what you put in was lost the day it was manufactured. This is because Vitamin C is a water soluble anti-oxidant, therefore, by design it is readily oxidizable. The phosphates essentially envelop and protect the ascorbic acid from being oxidized. Once in the gut of the fish (or any animal for that matter) , the phosphate groups are quickly cleaved by phosphatases supplying pure vitamin C to the animal. These diets are good for a year if stored properly. Once wet - they are highly perishable. Keep them as dry as possible. If kept dry, the first thing that will go bad is that the fat will oxidize. The good news is that you can easily smell rancid (oxidized) fat. Once you have smelled it, you can't mistake it. So smell the food. If it smells fishy - great!

If it smells like rancid fat - get new product and discard old.

As an interesting side note - if you look at Requirement estimates for Vitamin C - you wll see that the new estimates are less than the old. I think this is simply because most of the vitamin C was oxidized before the food was fed to the fish.

Freezing does not hurt, and will extend the life somewhat. However, care must be taken if you take food out of the freezer when it is warm and humid, water will condense on it and - as soon as food gets wet - it is highly perishable (and it will get moldy). So, make sure you have plenty
of air circulation if you do this.

The first and most important issue in food storage - keep it dry.
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Price:
All food prices are going up - most people put the blame on a combination of Ethanol/energy policy, rapid economic expansion of China and India, the US Dollar devaluation and speculative money funds pouring into commodities. A couple years ago, eggs were $0.79 a dozen in St. Louis, I just paid $3.49. Corn was in the $2 to $3.00 range for most of the last 30 years, it is now
over $6. A few years back Fish meal was $450 to $650, it is about $1000 now.
Some say the days of really cheap food are over.... I do not know.
Of course most commodities are seeing the same price increases. As mentioned on the thread - fertilizer is up even more, as much is imported(weak dollar hurts) and it is energy intensive to produce and move. Gold,Copper, Oil, Rice.... have also seen all-time highs recently.