cloudy water, fish breathing hard

Question
QUESTION: Hi Ron,
I have a 125 gallon freshwater tank.  It's been set up for over a year.  I have a Nu-clear filter system (with just the pleated filter in it), and one bubbler in the tank.  there is one power head directly from the filter that breaks the surface of the water.  i have lava rocks set up in a reef style.  i've never had to use activated carbon or any other types of systems in my filter.
I have 2 mature red tailed barbs (about 8 inches each, been in the tank since i set it up... my aunt gave me the tank), 1 rainbow shark, 5 tiger barbs (2 albino... i've had 3 die in the past day), 3 balla sharks (1 is about 5 inches long, and i've had these guys for a long time), 2 Jack Dempsy cichlids (new arrivals since last week), 2 cory catfish, 4 giant danos (new arrivals this week), 2 large catfish (light silver with black accents, very whiskery).
The water temp is set at 78oC. I tested the water yesterday... pH is att 7.8, ammonia, nitrate and nitrite levels are fine.  The fish are having a really hard time breathing.  they sit at the top of my water and "suck" in air from the surface.  The water has become increasing cloudy, even with a 25% water change, and a change of the filter.  I'm at my whits end trying to figure out what's wrong with the tank.  I've never had this problem before.  I asked a pet shop employee (a fish expert) what to do about the water, she said to add a clarifyier... made things worse.  Then they suggested i add carbon to the filter... not improvement.  They said it might be the nitrate and ammonia levels... they are fine according to the test i ran.
Can you help? Thanks!!!

ANSWER: Hi Katie,
  The water clarifier only clears the water but doesn't solve any of the root problems. Adding carbon won't do anything at all.

  Adding the Jack Dempseys may have a lot to do with the death of the tiger barbs.  Jack Demspeys are highly predatory and I suspect they will eliminate any of the fish smaller than themselves.

  Are the Jack dempseys also breathing hard?  If so, then it is a general tank problem. If not, then my guess is that the other fish are tired from being chased.  

  How often have you been doing partial water changes? You mentioned doing a 25% change, but when was the last one?  This is the most important thing to do and ideally you would be doing 25% once a week.  ON a large tank, you can cut that to about 25% every other week, but less than that you are taking big risks.

  Test kits are notoriously inaccurate. I never trust them.

-- Ron
  rcoleman@cichlidresearch.com
  Cichlid Research Home Page <http://cichlidresearch.com>


---------- FOLLOW-UP ----------

QUESTION: Hi Ron,
Well, the cichlids mostly stay to themselves... they chase each other around,
and leave everyone else alone.  I never saw them pick on the tiger barbs at
all... and yes they were breathing hard too (the cichlids).  That's what scared
me... because they were at the top of the water as well.  My large red finned
barbs were even breathing hard and they are normally very "cowish" in the
tank... swimming slowly, breathing slowly, bumping into each other and such.  
ALL my fish are breathing hard.
So, i've been doing 10% water changes everyday for 3 days now (to help
eliminate whatever is in the water that's making them sick without drastically
changing the chemicals in the water).  They seem to be doing better today as
far as breathing.  But now there is this weird almost slime-like red "stuff"
(looks like algae to me) on the rocks and shell gravel bottom, but i've never
had that in my tank.  Should i do a 50% water change?  or would that be too
much?  I usually do water changes every month (sifting through the gravel
and such) about 25-35% of the water.  The tank does have an under water
gravel filter (FYI).  Overall, today (after not feeding them yesterday night and
this morning for fear of a nitrate spike or something... just because the tank
is acting to weird), they seem to be doing better breathing wise, but i'm afraid
there is something really wrong with my tank.  I've invested in a Chembio-
zorb thing that's supposed to help with tank filtration and biological bacteria
set up and removing harsh elements from the water (i found it at
petsmart.com)... it's the same brand that i bought my nitra-zorb for the
tank.  I haven't put it in the filter yet though... it's on it way.  I'm just so
frustrated with this tank... i'm afraid really to do anything else.
Thanks for the advice... let me know what you think thanks!!

Answer
Hi Katie,
  Undergravel filters and cichlids seldom mix and here is why.  An undergravel filter requires that there be a uniform layer of gravel over it, to basically act as the filter bed.  Cichlids like to dig.  If a cichlid digs down to the filter plate and exposes it, then water will take the easy route and go down into the filter that way. Suddenly the rest of the gravel, that was having water sucked through it by the undergravel filter can become stagnant and VERY toxic.  If that is what happened, then you need to do some very serious gravel siphoning (using a proper gravel siphon) and I would change a lot of water, i.e., 25% for about 3 days running if you can.  

 Personally, I never use undergravel filters with cichlids.  

-- Ron
  rcoleman@cichlidresearch.com
  Cichlid Research Home Page <http://cichlidresearch.com>