"Pete" wrote in message
...
I have a tank 5' x 2' x 2' which has been set up for about 15 yrs and
contains community fish and is illuminated by 3 x 40W triton tubes (2
tubes on for 10hrs/day and the 3rd comes on for 3 hrs/day in the
middle of the 10hr cycle). The tubes are less than 1yr old.
*snip*
The tank was well planted, so much so that I had to remove handfulls
of plants every couple of weeks to keep it under control.
Excessive plant growth no longer occurs, probably because the algae
covers most of the leaves.

I'd like to know what plants thrive so much in low light (120w
flourescent over 150G tank?)
In either case, your algae growth explosion is due to either an excess or
absence of nutrients. With everything else you mention, sounds like
perhaps you had a prolonged pH crash which gave the algae the foothold it
needed whilest killing your plants. Thiving algae + excess nutrients (due
to plant die-off) + new, unestablished plants = algae-covered plants.

You make no mnetion of CO2 injection either. without it, your water is
low in CO2 in the first place. Advantage: algae.

Invest in some test kits to see what's going on in your tank. And how old
are these test kits you're using? Perhaps they're expired or faulty? Your
readings below show nitrIte of 10 ppm???? Pretty sure you'd have a tank
of dead fish. You're nitrAte results also are lacking. After 15 years
of enjoyment, surely, the relatively small cost of test kits is worth it.
with your stepped up regimen of water changing, you seem to have
stabilized the tank at least, however, issues remain. clean the
gravel/whatever you're using every water change. Some try to get all of
it, some pick sections and thoroughly vacumm it. Do what you need to in
your tank. Get rid of the undergravel filter..and whens the last time you
cleaned under the plates? You say it's less efficient..think you got some
major buildup under there? Yank those out. Your plants are dead/dying
anyway, no need to worry of roots entangled in the plates. this could be
where your problem lay. Nitrate "500" ppm really tells you nothing. You
need a more accurate reading than that.a pH crash will negatively impact
your biological filtration, as well as kill plants. Bacterial activity
takes a bit of a hit at/around pH 6.4 this and plant loss = more
nutrients for algae to utilize.

Test your water to see what's going in the tank. Test your tap water t
see what the tank system is doingto the water. Google for black brush
algae remedies. r.a.f.plants may be able to shed some insight also. If
you can and if you want to improve the plants, look at improving your
lighting situation and adding CO2 injection and fertilization. . (this
may be a chunk of change and the time to do some research so you don't
cause other problems)

Many plants died and I restocked just before Christmas, but many of
the new plants have subsequently died.

Plants have water requirements also. They have arange where they survive
and a range where they thrive. "plants" is pretty generic.

I live in a hard/very hard water area.
Water testing has shown the following-

on 3 May
Water temp - 79F
pH - 6.4
KH=TAC=Carbonate hardness - 3 degrees
GH=DT=TH - 21 degrees
NO2 mg/l - 10
NO3 mg/l - 500
After this test I changed 1/3 of the water and cleaned the substrate
in the filter and replaced the carbon.

on 15 May
Water temp - 79F
pH - 6.4
KH=TAC=Carbonate hardness - 3 degrees
GH=DT=TH - 21 degrees
NO2 mg/l - 1
NO3 mg/l - 500

A 12-day lapse in minimal testing when you know you have a problem is too
much. After your next water change, test the tank perhaps 1 or 2 days
later. See what's going on. compare it to your outgassed tap water. Old
tank syndrome should have much higher nitrate than this, unless lack of
biological filtration. NitrIte of 1.0ppm is not desirable, so even if you
meant 1ppm not 10ppm, this is an indication/symptom of problems. No
ammonia testing? With nitrite of 1, and nitrate unknown, you've more than
likely got ammonia at elevated levels also. Test your outgassed tap water
for all three. tear up those UGF plates and get rid of them (at least
look under them from the bottom of the tank with a flashlight) Should be
no need for it if you have heavily planted tank. Same with the carbon in
your filter. lastly, no real mention of fish in your tank. They
dying/dead also? Fish should visibly react to detrimental changes in your
tank before plants should, catch is you need to be able to recognize that
change in behavior, coloration, etc. Sounds like you had warning signs of
your tank's condition falling, now you've got a problem. determine the
*cause* of the problem and the symptoms resolve themselves. JMO

HTH
-lila pilamaya