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Re: RO water & algae problem

> I said that it was around 0.5 ... So it's actually around 0.1
> (according to the Red Sea kit), which is within the acceptable realm.
> But perhaps I don't want to be adding any more (?).

That is correct. 

> Do you know if the laterite in the substrate can leach iron into
> the water 

Initially it will raise the iron levels. 

> and give false iron readings?

No, they are real iron readings. 

> I know from a water analysis I got from my water company that my tap water
> contains 0.33 mg/l of phosphate,


> Either that or the test kit (Seachem), is inaccurate. I must say I'm
> somewhat suspicious of it. Should I bother with anything like
> Phosguard or Phos-zorb?

You should invest in a good phosphate test kit *before* you attack a
possibly non-existant problem.  Look into LaMotte (www.lamotte.com).
If you use an anti-phosphate agent, I would do it in a pre-treatment
container and not in the aquarium unless you know FOR SURE that it
ONLY removes phosphate and NOT valuable trace elements. 

> You also said nitrate levels should be around 5 ppm as opposed to 0.
> I can't find a test kit that gives nitrate readings that precise (My
> Wardleys dry tab kit will actually only tell me I have less than 10
> ppm, so I'm just assuming its 0 since I know my tap water doesn't
> contain any). I assume Lamotte probably makes one that exact, but are
> they the only one?

LaMotte and Hach (www.hach.com) are two sources of high quality test

> My CO2 level is 15 mg/l. Do you know if most people who use CO2 have
> higher levels of concentration than that?

15 mg/l is a very good level, so the powerhead method works well for
you.  Are you confident of that measurement?  Do you have a CO2 test
kit or are you inferring it from a table? 

> There was some discussion recently about the CO2/KH/PH table and its'
> accuracy.

The table is accurate but there are some assumptions made that may
render your results unreliable.  

The table is based on "KH" or the bicarbonate concentration in your
water.  Since bicarbonate can't be measured directly, there may be
some slight of hand used in kits like the Tetra KH test. It may be
testing total alkalinity.  This is fine IF bicarbonate is the only
source of alkalinity in the water or IF the test kit somehow
sequesters other alkalinity producing agents (like phosphates ;-) such
that bicarbonate is the only active source in the sample. This has not
been verified to my knowledge.

So, the CO2/KH/pH tables are accurate if, and only if:

1. Your "KH" value is truly a bicarbonate measurement,
2. Your "KH" measurement is accurate,
3. Your pH measurement is accurate.

Errors of +/- 0.5 dKH and +/- 0.2 pH units can give quite a wide range
of CO2 values in the table. Also, your interpolation skills may affect
the values depending on how the table is constructed (the table in The
Optimum Aquarium is particularly hard to use). 

Using a LaMotte narrow range pH test, a LaMotte CO2 test and a Tetra
KH test, our water parameters match the table exactly and are self
consistent.  We are pretty confident that bicarbonates are the only
source of alkalinity in our water.