Dead fish!

Question
Ron,
I have a 90 gallon tank with discus, curviceps, tetras, cory cats, and otocinclus.  Before the "crash", there were 15 cardinals, 5 rummy nose, 3 Roberti tetras, 5 silver tip tetras, 3 discus, 4 curviceps, 3 cory cats, and 5 otocinclus.  The tank has live plants.  I have had a problem with black fur-like algae on the wood and rocks. It doesn't seem to be getting any worse and I plan to scrub all the pieces soon.  I went out of town last weekend.  On Friday morning, I fed the fish as usual and left the light on for about two hours.  I turned off the light when I left home.  I returned home Sunday night and found many of the tetras dead.  There are only 7 tetras left.  The other fish are fine.  My pH is always quite low, even though I don't add anything to the tap water I use with water changes.  It's around 5.5.  I checked the pH and there was no change.  I did a water change and the remaining fish are fine.  Do you think leaving the light off caused the algae and/or plants to "do something" to the water?  Nothing else was different.  Any thoughts would be greatly appreciated.  Rather than trust a timer, I thought it would be better to leave the light off.   Would it better to leave it on for a weekend?

Answer
Hi David,
 I can be 99.9% sure that the light and algae had nothing to do with it.  I know the kind of algae you are talking about and it is no problem to anything.  In fact, lots of fish like to peck at it as food.

 Leaving the light on (or off) won't affect the fish that much. The light is mostly for the plants and for you.  The fish largely couldn't care less.

-- Ron
  rcoleman@cichlidresearch.com
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