R O

Question
A two part question. First: What is the easiest way to do R O for water treatment, anything short of buying a filtration system. Second: Strange behavior in one of my fish. In my tank I have a medium Sailfin(fish in question), flameAngel, firefish, pearlscale butterfly, blue damsel, 2 clown. These fish are a week old too the tank besides the firefish. Anyways the sailfin has been lying toward the bottom and even going on his side at times with slight rapid breath. I thought it was the end of him but shortly after he is up and swimming around like everything is fine. His behavior usually occurs mid-day for about an hour or two. He is eating fine as well with no visable signs of sickness. Is he just stressed or possible sick, been going on for 2 days.
Thank you your a great help

Answer
Hi Will. There is no easy way to make R.O. water other than buying a filtration system. This should be as essential a part of setting up a saltwater tank as the tank itself and the cost of them is totally worth it if you consider how many times the average aquarist goes through a problem concerning their water. With an R.O. unit in your house clean pure water is only a step away. You may be able to buy R.O. water by the gallon at your local fish store. And this is the next best way to provide your fish with the highest water quality. You can also buy distilled water by the gallon at most grocery store however if you have a large tank this can get quite expensive.(making the cost of an R.O. system pay for itself in a year)
First check your water quality to make sure it is okay. From what you said it sounds like you added all those fish, besides the firefish, at the same time. Unless you have a really large tank you should not ever add more than two fish at a time. Your biological filtration has to keep up with a higher amount of ammonia being produced and sometimes it may take a week or two to stabilize each time you add new fish to your tank. On the other hand some tangs(it is a sailfin tang you are talking about right?)will often lay on their sides when they are highly stressed out. Finding the reason for this stress is very important in keeping his immune system up. A stressed out fish weather it be from poor water quality, poor nutrition, or being picked on will eventually become a sick fish.
Check your pH three times a day for the next day or two. Test once when the lights come on in the morning, once in the middle of the day when the fish seems his most stressed and again before you turn out the lights for the night. Your pH should fluctuate a little throughout the day. Usually morning it will be at its lowest and midday its highest. Check just to make sure it is not fluctuating too high during these times of stress. If not at least you can rule that out.
Keep an eye on him and check your water once a day for the next few days. If everything checks out and he still is not showing any signs of illness but acting strange you may  just have a fish with a more nervous than usual personality. Fish are not all the same. They have very different personalities just like people do.