fish acting wierd

Question
Hello. After all my fish died last time I took a long time before getting more. I belive the problem was that I misjudged the size of the tank and over medicated them. I haven't put anything in the water except some liquid microbacteria, and just a bit of that. I didn't put anything in the water to declorinate it, I just let it sit for 5 days with the filter running. The water in Taiwan is very bad.
Now the problem. Yesterday when I got the fish they were all fine. I got two bottom feeders (yellow with black tiger-stripes) and some food for them. Today, I found one laying on the bottom of the tank and the other hiding under something. I turned off the light to see what would happen. The hider came out and started scutting around. The other perked up but didn't mover around much. When I turned the light on again, the hider hid again and the other flopped on his side. I've got the light off now, but the little fish (guppies?) are laying on the bottom when it's dark.
I've had trouble with fish and light before. I was keeping two newts in this tank with a small light just on one side. After a few days, the gravel and the decorations (little fence) had turned a burnt orange color. It cleaned off easily. I'm worried that there is something in the water that is reacting with the light. Or could it be the microbacteria that I added in?
Also, the one sick (non-hiding) bottom feeder's head looks black unlike the hider.
I don't know about the ph, nitrate, or ammonia values or how to go about measuring them.
Hope you can help, it would be quite depressing to loose any more of these guys. Thanks,
Nick

Answer
Hi Nick;

So sorry you lost all your fish. Very sad.

As far as your new fish, sounds like everything is pretty normal to me! Bottom feeders are often nocturnal and are active at night. During the day they hide from the light. They also have individual personalities. Even if they are the same breed. Some hide more than others. Color differences are normal too. They change with mood, weather, surroundings, etc. They might also just be stressed from anew home and will need time to adjust. If the "sick" one doesn't settle down and act more normal, get more hiding places. The active one may be hogging them and scaring the other.

The guppies are hiding at night because they are not nocturnal. They can't see at night so they rest when it is dark.

The rust color you see is simply algae. Wipe it off and make frequent water changes to keep organic wastes to a minimum. This keeps algae down because it is food for the algae.

Followups welcome.

At Your Service;
Chris Robbins