27-07-2004, 10:02 PM
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"The Estimative Index" contradicting with PMDD?
(BobWu) wrote in message . com...
My fish tank experienced all kinds of algae problems in past a few
months. I started PMDD practice, now I have virtually zero phosphate,
5-10ppm nitrate, and 15-20ppm potassium. All other types of algae are
now gone, but the hair algae still linger. I thought they can not
survive on zero phosphate?
You don't have zero PO4, you have a cheap test kit. But even with the
best test kits around, you still are beyond their limits to measure
and PO4 limitation on algae. I am and I have a research lab.
I then got a few SAE from internet, they look exactly like the true
SAE pictures I found, however, I found them eating fish flakes instead
of hair algae. My Oto work much harder than them.
Since the fish couldn't control hair algae, I'm back to internet to
try to find a solution, now I found Tom Barr's "The Estimative Index".
It says you should have 1ppm phosphate in water volume. Now I am very
confused, isn't PMDD's goal to make phosphate a limiting factor? Am I
missing anything?
Limiting but not absent, 0.0ppm is bad for plants. As long as there is
enough for plants, you are fine, but it does assume excess PO4 causes
algae which is incorrect in our situation(lots of plants, shallow, CO2
enrichment, warm stable temps etc).
Also, when you folks prune stem plants, do you cut them back in half
or even more?
Generally I trim about 1/4-1/3 off the bottom.
FYI, my tank setup is,
75G, 240W, all flourite substrate, CO2 tank, PH=6.7, KH=4, GH=11,
N=5-10ppm, P=0ppm (0.25-0.5 immediately after water change),
K=15-20ppm, Iron=?, temperature=79F-82F (will be lower in winter), I
don't add extra trace element (because I discovered that whenever I
added flourish, I got hair algae bloom), planted in almost every inch.
You can keep the pH at 6.6-6.7 during the entire day, this will go
along way to keeping algae from coming back.
Would the limitation of the PO4 also not affected the plants far more
since they represent perhaps 50-200x more biomass than even a fairly
well infested tank?
You cannot limit the algae without removing and not feeding fish,
having the plants in there and their dying leaves leak
PO4..........organic forms of PO4 also are consumed by algae wereas
plants can only use inorganic forms of PO4.
Algae, specifically the periphyton from warm water are not limited at
3ppb, that's beyond the testing limits of laboratories..........I
doubt your little old test kit is going to tell you what you need to
know relative to the algae.
Paul and Kevin based their assumption on PO4 limits algae and this is
the way to control algae blooms.
If I have 1ppm, do you think either the plants or the algae are
limited?
Certainly not.
The plants pearl like mad after adding PO4. Within about 30-45
minutes.
As long as you have good CO2, NO3, K, GH, traces, this addition will
drive your tank's growth rate up and also increase the NO3 consumption
by 2-6 times depending on the intensity of the PO4 limitation.
Your tap water likely has some PO4 in it. So you might need to dose
once or twice during the week.
Folks have gone up to 2ppm for extended periods, no algae.
So if this assunmption is correct(PO4 excesses cause algae), why don't
I have algae? Do you still think it's true? You have algae and almost
no PO4, I have lots of PO4 and no algae.
I'll let you decide which is correct based on your own observations.
BTW, I add roughly 15mls of flourish to my 75 Gal every other day with
no algae also, I have a little more light but the same results will
occur with 240 watts etc.
You select for the algae when you take away the PO4 for the plants.
Grow the plants, and take of their needs and then you do not have
algae.
They need more PO4 than algae. A lot more. Dry weights of FW algae are
around 14:1 N:P, for aquatic submersed plants: 10:1. These are general
averages.
Regards,
Tom Barr
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