Fish food can be one of the more expensive components of operating a large aquaponics setup and ways of cutting the cost of food and producing your own food generates a lot of discussion on the Aquaponics forums. When I first put in a tank I ordered a 20kg sack of food from a Brisbane retailer which cost about $60. The problem with doing this was that it became clear that the cost of freight added to this was going to make food purchasing an expensive option.
The third time that I rang up to make an order curiosity got the better of me and I asked what the bulks sizes of food delivery cost. The sales man told me that they could provide pellets in half ton or full ton pallet deliveries. I got all of the details and said said I would call back later after I thought about it.
I went looking for information on the net about how long feed pellets last and rang a friend who runs a commercial Barra farm to pick her brains. She she told me that she had once bought a ton of feed and put it in a feed bin in her shed but that it only lasted about 8 months.
The comments on the net were similar which was a problem as I needed the food to last about 3 years to make it worth while.
Some more research led me on to the idea of vacuum sealing food in Mylar.
This is a method of long term storage that can be done at home without any special equipment, you just add the food you want to store, throw in a couple of oxygen absorbers and then use a house hold vacuum cleaner to suck all of the air out of the bag before sealing it with a clothes iron.
Finding the bags wasn't as easy as I thought it would be but, although being a very common method of storage in the United States the bags didn't seem to be as readily available in Australia.
I ended up ordering some through Ebay and had them shipped here at a cost of around $3 per 20kg sack.
Packing was a simple process, I made sure that I put a pump filter sock over the end of the vacuum cleaner so that it didn't suck any of the pellets out and then started transferring the feed from the original bags to the mylar.
There were a couple of tricks that I quickly discovered. The first is that the seal on the bottom of the bags is only about a cm away from the bottom edge which means that if you move these large bags too roughly then the seal can break and the bag will depressurise. This was easily fixed by running the clothes iron along the bottom before adding feed to give the bag a good 10 cm of seal which seemed to hold well. Care was still needed when relocating the sacks but it seemed to work well.
Another thing I found was that the top of the sacks have an envelope type fold and after being ironed shut didn't hold a perfect seal. This is can be avoided however by pressing the edges of the bag true against each other rather then using the folded seals, this method has held a good vacuum seal for the last 18 months.
After the feed is added to the bag open a pack of O2 absorbers that come with the mylar bags and throw a couple onto the top of the feed. Seal most of the top of the bag with a clothes iron but leave space to put the nozzle of your vacuum cleaner into the bag. Once all the air has been removed, quickly remove the nozzle and seal the last part of the bag. It should now be rock hard and can be date stamped with a marker pen and moved to a storage location.
If any of the bags lose their hardness within a few days you can reseal them but I just use those ones up first and leave the best sealed ones to last. Storing the bags inside PVC buckets is a good idea if you have a rodent problem in your storage area. I often pick up second hand buckets from the Farmers coop for a few dollars each, they normally have had a food stuff like yogurt in them previously and are easy to clean. Bucket storage makes them easy to move around as well.
I have had the bags stored for 18 months now and the quality of feed has been excellent in each bag that I have opened and I have so far only opened the worst sealed ones with the best seals being left to last.
The total cost of feed, delivery and mylar storage adds up to about $50 per sack which is more then $30 dollars a sack cheaper then it would have cost me to buy the feed one sack at a time.