js1 wrote in :

On 2005-01-20, Pete wrote:

I've had an algae problem in my 90gal with a similar setup. It's not
a Phophate problem, you can try and limit phophates but you'll notice
all your plant growth slow down which means less competition for the
algae (been there, done that).
Algae loves crap.. yeah the stuff from the fish. NH4, urea etc. That
heavy fishload will be causing the same problems as mine are (big
fishload also).

I'd recommend doing what you already did for plant cleanup (a dip in
chlorine, H2O2 etc) to get them free and a head start, but I would
also do a large water change with a massive gravel vacuum. When I
pulled up all my plants for a cleaning I did the water change at the
same time and vacuumed all the gravel hard and deep until it was
clear. So no more crap rotting and that about fixed it in one shot...
it's in my books now as a bi-yearly (?) thing as long as I keep my
present fishload.


Well, now you're arguing a causality problem. I can't give a
scientific explaination, but I'd have to guess the phosphates are
feeding the algae. The algae is growing so fast that it's also taking
up the nitrates (produced by the decaying stuff) as well. My guess
would be by backing down on the phosphates, it slows the growth of the
algae, and gives the plants a chance to fight for the nitrates.


Yeah it's not an easy discussion as unless you are doing scientific
tests you can talk forever on what is or isn't causing your problems...
and since there are so many variables in your basic tank it a big
discussion.

The main reason I think (imo) it's not excess phosphates is I've been
down the route of limiting P before. No P ferts, P absorbing packs in
the filter etc. I still have small amounts of algae now (in corners
etc.) but my higher than 'official' recommended levels of P don't cause
any problems (I fert with P regularly) so I don't believe it's P alone
that causes a problem. Lowering P will reduce growth rates but it does
it for everything, plants included, so it still doesn't allow your
plants to out compete the algae. I've also added large amounts of P to
my tank to get levels way above the recommened and no huge explosion,
but add some urea (like accidently uprooting a mostly N jobe fert stick
made with urea) and boom.

So instead I've suggested the gravel cleanup (fish reduction would help
also but if you want lots of fish.....) on the principle that algae
thrives due the NH4 and stuff from the fish. So excess NH4 and some P
gives you a big problem, but why hit the P that both algae and the
plants you want to grow use, but not hit the NH4. Keep the P that plants
(and algae) need to grow well but try and hit the NH4 that seems to the
real algae favorite but the plants can do without. On that note adding
more plants and quicker growing plants (I love floating water lettuce)
helps.

P.

BTW. this is for a CO2 inj high light tank, non CO2 regular lighting
fert requirements are quite different.