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Re: Aquatic Plants Digest V2 #1120

Subject: Re: Plants whilting and Sword deteriorating - Need help
>Thanks for that comment - a useful piece of information for me at the 
>moment. Here in "Sunny Queensland" in Australia (other hemisphere, 
>heading into the height of summer), I actually struggle to keep 
>temperatures below 82 degrees, 

You _can_ still have excellent growth at that temperature... I've kept
planted Discus tanks at that temperature with no problems.  But everything
happens faster, and you really have to keep feeding.

>and I can get them as high as 88-90 
>_without_ the use of a heater if I don't watch it (and Brisbane is in 
>_southern_ Queensland - I don't want to move north!). Open top tanks, 
>fans blowing, and lots of evaporation are essential.

I had a period of about 6 weeks once here in New England (where no one has
air conditioning 'cause it "never" stays that hot for long<g>) where my
tank temps. hovered in the  low 90's.  While a few plants only hung on
during that period, many did just fine.

It's not the easiest way to grow plants though!<g>


Subject: Re: Nutrient limitation

Dave wrote:

>Any nutrient can be used as a limiting nutrient, however;
>It is difficult to have an algal free N limited tank because blue-green 
>algae can fix N2.

But isn't it possible to limit N in the _water column_, while still not
allowing N to be limited in the substrate?

>It is relatively difficult to have an algal free Fe limited tank because it 
>is a micronutrient and therefore small amounts can produce large algal 

I agree.  I wouldn't want to use this method.  I suspect it would only work
under fairly low light conditions.

>IMHO, the easiest to use as a limiting nutrient is phosphorus. It is used 
>in relatively large amounts by plants and can easily be omitted from 
>water-based plant fertilizers. 

But it is also added to the tank every time you feed your fish.

>Having said that, its important to 
>understand that macrophytes can in no way outcompete algae for P. Algal 
>uptake kinetics are such that they can drive the P levels far lower than 
>macrophytes can... after discussing this with Sears and Conlin and 
>thinking about it for a few months I came to the conclusion that the 
>algae become P limited because the TURNOVER rate of P in algae is much 
>higher than in macrophytes. As the P becomes available (through algal 
>senescence) the macrophytes 
>sequester just a small amount but keep it much longer so that over time 
>the algae eventually lose out. This is at present not supported by any 
>research that I know of.

Sounds reasonable.

>Diana's systems of course are sediment based and allow the removal of 
>BOTH N and P from the water column... a strong argument for fertile 
>substrates in my mind... of course you cant have non-rooted plants under 
>these conditions.

What I found interesting about her tanks was that they were _not_ N and/or
P limited in the water column... they were really rather high.  Of course,
I can't say for sure that her tanks are regularly free of problem algae,
but they all looked good when I saw them.  The impression I got from her
was that she didn't have any major algae problems.

Karen Randall
Aquatic Gardeners Association