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Trying to advoid algae blooms

At Sun, 8 Oct 2000 22:22:13 -0500 , "Len Kutz" <len at kutzfamily_net> wrote:

>Currently my nitrates are close 6.  Not bad, but they were 12 just two weeks
>ago, and I have not done any water changes to get them down.  Phosphates are
>about .75.  The plants are growing so fast I can't believe it, but I'm
>afraid the green water is just around the corner.  I've never measured Iron,
>Potassium or any other trace elements so I have no idea if they might be a
>problem.
>
>Does it sound like I should be adding small amounts of nitrates to my tank?
>If so how should I go about doing it?  I'm not a chemist so please keep it
>simple.

The goal is to have enough Nitrogen, Phosphate, Iron and other 
nutrients to meet plant needs without having enough to trigger an 
algae bloom since all 3 are essential to both plants and algae. 
Ideally the plants will outcompete the algae for these nutrients so 
you get plant growth without algae blooms. That sounds exactly like 
what you're reporting so you've got reason to smile at present. If 
the plants are growing, they're getting enough so no need to worry 
about whether something is a problem at present.

As far as adding nitrate goes, plants prefer ammonium, the NH4+ ion, 
to nitrate NO3, so they won't start to reduce the nitrate until the 
ammonium is all used up. Since ammonium is an earlier form of 
nitrogen in the cycle, nitrate won's start to build until you have an 
excess of ammonium, and won't start to reduce until you have a 
deficit of ammonium, all other things being equal. As long as you 
supply enough nitrogen for plant needs and there isn't enough left 
over to trigger algae, fine. I'd just keep an eye on things at the 
moment and see how the tank progresses. If the nitrates drop to zero 
and plant growth falters, I'd consider adding nitrates but not until 
then since the nitrate reading, if it's above zero, indicates a 
reservoir of nitrogen available for use as required. The fact that 
it's currently dropping means either the plants are using it because 
there's not enough ammonium, or they're still getting their nitrogen 
from ammonium in the tank and other factors - better tank 
maintenance, whatever - are causing the fall in nitrates. That's the 
reason for the "all other things being equal". It's hard to say 
whether the nitrates are dropping because the plants are utilising 
them after consuming all the ammonium, or because something else is 
reducing them on the basis of the info you've provided, hence my 
recommendation for a watching brief on the situation.

It's possible that the algae bloom was caused by the combination of 
nitrogen and phosphorus, or it could have been iron or something 
else. Some systems - Dupla's, for instance - rely on algae control 
through limiting iron and there are a number of scientific studies 
showing algae blooms being triggered by adding iron.

Whatever, I think that it's fair to say that if the plants become 
limited in any  nutrient and there is an algae present in the tank 
that is capable of better utilising the mix of nutrients you have 
than the plants are, then the algae can get a go on. If you remove 
the limitation on plant growth, the plants should out compete the 
algae again and that's the balance you're trying to maintain.

My advice - the plants are growing and algae isn't so keep an eye on 
it and watch what happens. If the plants start to slow, consider 
adding nitrogen or iron - you may have to get an iron test kit to see 
what level iron you have and whether you need iron more than 
nitrogen. PLUS, and it's a big plus, enjoy the fact that you've got 
it running well at present. That's what we all aim for at first and 
then we learn to juggle things to keep it running well. The juggle 
can change over time and different algaes can start to get a move on 
- it may not be green water.

I think everyone gets some algae from time to time and we tinker in 
various ways until either it goes away, we accept it and live with 
it, or we give up keeping tanks. I know a person with a great looking 
tank with a pile of algae, but it's nearly all green algae growing on 
a piece of driftwood and it doesn't grow anywhere else. The driftwood 
looks great that way - very natural - and he hasn't been able to find 
a way to eradicate it so he's quite happy to have things stay the way 
they are and the tank always draws positive comments so algae needn't 
be a complete no-no.

If I had to suggest an easy source of nitrogen, I'd recommend Tetra's 
"TetraPond Flora Fin". It's a liquid fertiliser for ponds that 
contains 1 part nitrogen to zero parts phosphorus to 6 parts 
potassium - that's 0.5% nitrogen and 6% potash. I'd start at a 
quarter of the recommendation for ponds and slowly up that depending 
on how the plants pick up and the results of your nitrate testing. 
You want plant growth with a low but stable rather than rising 
nitrate level. This probably isn't as cheap as some other nitrate 
sources but it's incredibly convenient and the pond dose 
recommendation is 1 ml per 200 litres every 2-3 weeks so it's 
concentrated enough to ensure a 500 ml bottle lasts a reasonable time.

David Aiken