Now I'm feeling really guilty...
I keep promising I'll put together my "cheap prefiltration system" article and then don't do it. Here's a short (sort of) rundown:
Colin and Greg know what they're talking about (know more than me, too!), octos are notoriously sensitive and a Reverse Osmosis and/or Deionization system is the way to go. These are expensive. The most direct alternative, buying water, is more expensive in the long run. You can possibly get RO/DI water from your LFS. Or, you can get it from one of those kiosks in your local grocery store, the kind you push a button to fill up a jug that you bring.
One day I may get an RO/DI system. But since I was on a tight budget and balking at the RO/DI approach, I did a ton of desperate research. I finally came across a system using a PolyBioMarine PolyFilter. PolyFilters are well-respected in the aquarium hobby--they absorb lots of "bad things" from your water, much like activated carbon does, though supposedly they absorb a broader range of things. They have many interesting qualities I won't go into right now. THey look like standard plastic-based, coarse mechanical filtration pads, but they are impregnated with a special chemical combination that lets them absorb (and under the right conditions, release) lots of unwanted molecules.
I assembled my filter out of PVC pipe (about 2.5 inch diameter,) a PVC endcap, and silicone sealer. I cut a roughly 18 inch segment of pipe, attached the endcap, sealed it with silicone, and drilled a large hole in the endcap. Then I rolled up a sheet of PolyFilter across its shortest ends so the roll would be longest, and stuffed it into the pipe. You end up with what looks like a jellyroll. I attached a faucet-mounted carbon filter to my kitchen faucet (made by PUR.) I place the filter in a bucket, the bucket in the sink under the faucet, wedge the filter so that it stands up and catches what runs through the faucet, and run water through the PUR filter into the homemade filter. The water accumulates in the bucket.
This is a terribly inelegant system, and I could do much better on a second try. But it was cheap--putting this together should cost you less than $40.
BUT! There are problems here. PolyFilters are good, but they DON'T remove everything an RO/DI system does. Worse, it's difficult to find precise (or readily accessible to non-water-chemists) information on what they DO or don't remove. Thus, these are risky. They might work pretty well, but depending on what's in your local tapwater, they might not. I have had NO problems at all, my octo was quite happy with this system. I suspect that will usually be the case, I think most people's tapwater is good enough that these systems will work fine, but I CAN'T promise that.
If you're interested, check out this link:
Petco: Pet Supplies, Pet Food, & Pet Products
These guys carry a pre-made filter from the company that uses PolyFilter discs. Some forms of PolyFilters are stronger than others, and I thought I'd heard the discs are. This has the added benefit of not having to build the filter! Since I've been quite happy with my system I might get one of these...originally I had even read a review of this system on about.saltwateraquariums, but couldn't find the system to buy. You can also run a search on this site for "PolyFilter" and find the other forms of the filter media.
Again, let me stress: RO/DI is THE way to go, if you can afford, you just MUST get it. If you can't afford it...sometimes you STILL must get it. I just can't promise that PolyFilters will work. But you can give it a try...if snails and maybe a sea slug survive (that was my "guinea pig") then maybe you're octo-safe.
rusty
