I can't speak for everyone, but I've noticed that you've got a curious balance between things that you've prepared for extensively, and things that you seem to want to rush or cut corners on. You've done a great job of researching a lot of aspects, but when something catches you by surprise, you seem to rush through dealing with it rather than taking a step back and assessing the situation. Of course, neither of those approaches is always the right answer, and I tend to lean toward the "taking a step back" too much of the time. I think, though, that people are concerned that you've put all this thought and effort into your tank, but you're at risk of running into problems from the water you're using... unfortunately, sometimes a project where you do 90% of everything perfectly can be undone by critical problem in the other 10%. I also know that you've been very much trying to make sure you can do this within your budget, so the "argh! I have to spend money on *water*, too!" response is completely understandable.
Trying to take a step back, I think it's worth looking at the pros and cons of the various water choices, and maybe asking if there are any other possibilities you haven't considered.
1) city water or well water
pros: it's free or cheap, it's right where you need it, so you don't have to transport it
cons: it has just been tested for human consumption, so all sorts of stuff humans don't mind that kills octos could be in it. Also, it's probably chlorinated and deliberately messed up. Also, it may have passed through copper plumbing, which, while it might not add enough copper to cause problems, is an unknown risk
2) wal-mart distilled water
pros: it's not too expensive, it's available, it should be a lot more pure than regular water
cons: it's not intended for aquariums, it's intended for uses like car batteries, so there may be some stuff that's not good in it. And you have to lug 50 or so 1-gallon jugs back from the wal-mart, and another 10 or so every time you want to do a water change, and keep some on hand for emergency water changes and top-offs.
3) finding a local source of RO water
pros: convenient, local RO water is what you really want, if you can get it
cons: it might not exist, and if it does you haven't found it. It also might be more expensive than the distilled water.
4) buying a reverse osmosis unit
pros: this is the best possible solution, because you can turn your city water into RO water. Of course, it takes a while, but since you're short on money, that's probably fine, and most of the time you can sit around and play computer games or read TONMO or whatever while it's filtering.
cons: this will be a big up-front investment to save money in the long term. Some random site I found on google (
Water Filtration Products Catalog – Pure Water Products, LLC ) says they sell theirs for $368, some are as cheap as $189, and some are as expensive as $1300. Obviously, they want to sell theirs, so take that with a bit of skepticism, but let's say you can get one for $400. I think you said the wal-mart distilled water was $0.68/gallon, so that's around, oh, $35 to fill up the whole tank, or $4 for a 10% water change. So if you expect to do 100 water changes, or, say, 75 water changes and a few more major changes and a lot of topping off, a $400 RO unit starts to sound like a better investment.
That's just my first cut at looking at the big picture, I may well have missed some possible options. I think the concern a lot of folks are expressing is that it would be a shame if your octo is harmed because you've got a great setup but you saved a little money on the water in a way that proves unhealthy for the octo. Setting the budget for stuff like this is one of those skills that's pretty hard, and often needs a surprising amount of "slack" planned in to take care of things that come up... I know you've been trying very hard to both stretch your money to make it work, and to set up a very good system for an octopus, and that's a very hard set of constrains to balance. I think we all want to help you succeed, but we don't want to encourage you to move ahead if there might be problems that could wreck the whole project... This is the sort of thing where
all the parts have to be in the "good enough" range or it'll work out badly, so the ceph care advice around here may sometimes come across as frustrating, but it's really intended to keep the "learning from mistakes" part of learning anything this complicated from hurting or killing your octopus.
Sometimes, it's pretty frustrating to spend a lot of time on TONMO trying to help people out, since a lot of people come through looking for a quick and cheap answer, and get mad (or just never post again) when there isn't one. I know you've made a good effort to not give up or stop listening when you hit frustrating points like that, so I want to acknowledge you for that, and make sure that you see this as us trying to be helpful in being realistic and successful, not trying to be discouraging. I'm really hoping you'll find a way to make this work, but I really don't want to see you spend all your money on something that almost works, but ends up leaving you with a bunch of expensive equipment and a dead octopus... Of course, I'm one of the least experienced staffers with respect to actual octo-keeping, so really listening to Nancy, Carol, Colin, Cuttlegirl, Jean, D, Thales, Paradox, and Dan (and I'm sure I'm forgetting some) is better than listening to me, but I'm pretty sure they all have the same main goal.