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Phosphate limited tank??

Pete <peteal at sympatico_ca> wrote:

> My problem is no I never have ANY phosphates in the water... I always
> read 0 (no P in tap water).  Now while there is no algae growth other
> than spot algae the plant growth is nothing special. I'm not using the
> phosp-sorb anymore and the fish/food doesn't seem to add enough P.

While I'm no chemist (nor do I profess to be an expert), this sounds
familiar.  I've written to this list recently about my own experience adding
phosphate to my aquarium and I've been party to more than a few off-list
discussions as well.  I've come to the conclusion that one must move from
general to specific (large to small, macro to micro).  This means that
before playing with phosphates, one should get a handle on the largest items
first, such as lighting, CO2, and N (not to mention GH, KH, pH, Fe and K).
If all of the above items are in balance and a tank is truly
phosphate-limited and plant growth is stalled, then CAREFUL phosphate
addition might help.  That's what I just when through and I've succeeded in
accelerating my plant growth dramatically with the added benefit of
producing a dandy bumper-crop of hair algae in the process. <sigh>

> My tank is 87 gal, 2x 175W MH lights, fertilize with PMDD, KH 8, GH 4,
> PH 6.8, NO3 10ppm , PO4 0, Fe .1, and DIY CO2 injection.
> My problem is that the N increases over time.  I had hoped that the
> plants good growth would keep the N down but it seems with no Phosphates
> they don't grow fast enough and the N rises.

Understanding where Nitrogen is coming from and the impact of adding
nitrates should probably come before monkeying with phosphate.  It seems
like you need to identify the source of your nitrates.  Plants love N,
especially in the form of ammonia, most often introduced as fish waste.  If
you've got a heavy fish-load, that could account for it.  Check your PMDD
composition carefully.  Roger Miller has written frequently about the
dangers of using terrestrial plant fertilizers in aquaria, specifically
relating to urea as a toxin.  VALIDATE YOUR TEST KITS!  Making decisions
based on poor-quality test kits is an amazing waste of time and money.  Good
test kits can be expensive, but they pay for themselves quickly.  The types
of kits that are needed really depend on one's local water source and what
has to be done to it to ready it for aquarium use, but a good initial set
would include GH, KH, pH and NO3.  The next level would include PO4 and Fe.
I haven't yet reached a point where I need more than those.

> So I'm think of trying the following.. (here is where I need the hints!)
> - - Starting to use TMG fert.  Thinking maybe I'm missing some micro
> nutrients although I had hoped they would be in the tap water (no growth
> increase when doing a water change)

I can't argue with this - TMG has proved to be a very good fertilizer for

> - - Using Jobe's sticks in the substrate. Question! The Jobe stick
> recommended is LOW in Phosphates... since this is where I think the prob
> is wouldn't I want low N and high P?? Already have enough N in the water.

Don't forget, substrate fertilization and water-column fertilization are
largely discrete.  It seems like most of the plants we cultivate derive most
of their nutrients from either on or the other.  I once placed 8 Jobes stick
into my substrate (before I realized that one or two was closer to what I
should have been using) and saw absolutely NO nutrient leakage into the
water column.  Of course, the nutrients might have all been sucked up in the
ensuing plant-growth orgy - your mileage may vary.  In other words, you may
not see any additional N in the water column.  In fact, there are those who
fine the typical houseplant Jobes stick (NOT reduced P) work beautifully.

> - - Adding Phosphates directly to the water  while making some sort of
> live sacrifice to the fish tank god not to bury me in a tankwide coating
> of green furry stuff.

This must be done carefully.  I find that I'm adding 1/8g K2PO4 to my 50gal
tank every two days, usually with 1/4 to 1/2 tsp of nitrate.  This small
amount of phosphate is still probably more than I need, and I'm still
attempting to hone in on the the right N:P proportion for my tank.  As I've
said in earlier posts, when I miss that right proportion by even a little
(either way - too much PO4 or too little) I see an immediate increase in
algae production in either GSA or hair algae, depending upon which way I

I've been offered this advise many times, though have only taken it
*	Take small, careful steps, changing only one thing at a time.
*	Wait a long time between actions to establish a true evaluation of
	your previous action.
*	Be prepared to perform large water changes if something pans out
	differently than you had hoped!

michael rubin
michael at rubinworld_com