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Re: Phosphate limited tank??

On Sat, 4 Mar 2000, Peter wrote:
> 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.

With a KH of 8 and pH of 6.8, your CO2 is 35+ mg/l.  That's pretty
remarkable for DIY CO2, but do you really want it that high?

> My problem is that the N increases over time.

I'm not a PMDD guy, but it seems to me like the most direct solution would
be to decrease the potassium nitrate content of your PMDD mix.
> - - 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)

The PMDD should provide all of you micro nutrients.

> - - 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.

Jobe's sticks work best for supplementing specific, heavy-feeding plants.  
They aren't a great solution for nutrient shortages or imbalances that
effect the whole tank.  You can get Jobe's sticks with different N-P-K
values - you can get high-P formulas if you want.

> - - 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.

Hagen's "PlantGro" fertilizer (someone in marketing there at Hagen leans
real heavily toward incipid names for their products) contains a small
amount of phosphorus; according the a letter they sent me a while back,
the guaranteed analysis is 0.3-0.08-0.8.  You could add a dose of that
stuff, and if phosphorus is the problem this should give your plants a
kick in the butt.

You might also try a *small* dose of a phosphate-based pH buffer.  For
instance, Greg Morin told us some time back that SeaChem's phosphate
buffers used as directed gave 80-100 ppm of phosphate; to dose your
tank with 0.1 ppm phosphate you would use 1/1000th of the directed dose.

More generally, adding phosphate in any form is at best an indirect
solution for a high nitrate problem, and may not solve your problem at

Roger Miller