I have been lurking since near the beginning of the digest and want to
express my appreciation for all the good discussions. Before the PMDD
thread, I noticed potassium deficiencies of plants in a tank of mine,
especially if water changes were bi-weekly instead of weekly. This is my
only tank with a mostly gravel substrate. The fertilizer talk comes just as
this tank has become very well established. What follows are some
observations of this system. The post turned out to be a little longer than
I expected.

                        Tank Description:  
-up for 18 months, 45 gal long
-substrate is medium aquarium gravel, UGF with powerhead (no air injection)
in          one side and several laterite balls and a 4" square of peat
plate in the         other side
-high fish load, moderately to heavily planted
-DIY yeast CO2 fed into a Whisper 4000 W/D filter on the back
-lights are 2 x 40 wt daylight florescent and 1 x 30wt GE aquarium/plant
-50:50 mix of deionized water and high GH well water, ph 7.8 with (CO2)
-Flourish added once or twice weekly per instructions
-Florapride added with water changes 1 1/2x instructions to compensate for
DI         water
-KH 10,  GH about 260
-NO3 30ppm (well water contributes av. 10ppm of this)
-P04 5ppm 
-Fe less than .5ppm (Lamotte test)

Plants: H. poly, Ludwigia, Val., Anubias, Bacopa, Rotala rotundifolia, Java
fern, Apongeton crispus, Crypt. wendtii, C. affinis, C. sp., and another C.
sp. All are doing well except the C. affinis. I put a little piece of peat
plate and a laterite ball right under this plant, away from the UGF, just a
couple of days ago hoping for some improvement.

Algae: even with elevated PO4 and NO3, my algae problem has always been
minimal; there is some spot algae and some very crusty red stuff on the
Anubias and I scrape some haze from the glass every 6 weeks. I have 3 SAE, 3
otos, 1 small pleco and some red ramshorns. I consider myself lucky, not
smart on this count. 

Rationale for using Florapride (FP) in this tank: I started adding FP
several months ago because the stem plants always showed signs of K
deficiencies and slowed growth if the water wasn't changed weekly. FP
contains mainly K and Fe, both of which I need in excess of that provided by
my water and Flourish. Other macro nutrients are plentiful (C, H, O, P, N,
S) as well as the micros Mg and Ca. FP is convenient and not all _that_
expensive. I have access to the chemicals, so I might make my own some day <g>.

Concerning transitory Fe levels: I raise the Fe level to ~.25ppm initially,
it decreases to between .1 and .2 in a week, then to about .05 at the end of
two weeks, so my measurements indicate iron is utilized or oxidized rapidly.

The K deficiency: Because iron levels are high enough with the addition of
FP, I recently started adding small quantities of my own K2SO4 soln. with no
apparent change in algae.  If I can get organized enough, I would like to
add measured, increasing amounts of K2SO4 on a regular basis while
monitoring P, N, and plant/algae growth. I just started monitoring PO4
levels, so I  don't have a baseline yet.

With only small amounts of peat and laterite, these plants are obtaining
most of their nutrients throught the water column or water circulation
through the gravel plus any mulm settling into the gravel. This should make
the K additions easier to evaluate.  

I share the frustration of not having a K test kit. Knowing appropriate K
concentrations and the rate of uptake would be beneficial with my water. I
am hoping that N and P will gradually be reduced, at which time I should be
able to formulate a K/Fe additive that will replace the FP, reducing my cost
merely to the time it takes to make it and the energy to fuel my body to
carry it home. Come to think of it, Tetra might be cheaper 8-). 

Comments:  All are welcome, gently please!!  

Dorothy Brandon         Davis, CA