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[APD] Re: too much PO4 or not enough CO2?

> Tank is 30g.
> Water changes done weekly at 50%. During that time, I also
> add enough baking powder to maintain kH of 5, add amounts
> of K2SO4 suggested by Tom, and 20ml TMG.
> Tapwater: NO3 = 8.8 ppm, PO4 < 0.05ppm.
> These measurements taken in the evening about 3 days after 50%
> water change.
> - pH around 7.
> - Nitrates (NO3) at 13.6 ppm.
> - PO4 > 1ppm (my kit does not go higher than 1ppm)
> - CO2 is around 15ppm

Basic issue: CO2, CO2 and CO2.
Not enough. The rest will fall into place if you add more CO2 for the ENTIRE
light period(20-30ppm).

Time and time again, even the best of us get dogged by not checking this or
not having enough.

Surface scum will even form faster/greater when less CO2 is present.
I've seen a correlation between these two for a number of years.

Not enough CO2= more surface protein/scums.
The plants likely leak this out in sub optimal conditions and/or the extra
CO2 drives photosynthesis faster creating more O2 that fries the

> I'm guessing the large PO4 reading are coming from fish food
> and waste. I also suspect it's causing the growth of spot
> algae on the tank glass and plants. (I didn't think I was
> feeding them too much food. And can someone tell me how to
> judge the right amount of food? Not what they can eat in
> 3 minutes, that does not work. My fish inhale their food in
> seconds.)

Or a bad PO4 kit?

> Is it safe to use a phosphate-removing chemical (like phosguard)
> in the tank to reduce the phosphate to more therapeutic levels?

Water change, heck of lot cheaper.

> Or are there other alternatives to reducing the phosphate.

Floating plants like water sprite.

> What about increasing CO2? I'm very worried about doing this
> because it could harm the fishies.

Not too much of an issue unless you really get up there.
With high O2 levels, the fish do pretty well, so focus on the plants, the
fish will be fine.
Your pH test kit is hopefully a pen/probe/narrow range since this is a
critical part of CO2 measurement.

The 20-30ppm CO2 range I've been telling folks factors in a large variation
of pH/KH test readings. 10ppm + or - is about as a wide range as I can
muster and still keep it good for both fish/critters and plants.

Remember you don't need CO2 at night, so crank it during the day.
Some worry about pH flux at night. I really don't think this matters at all.
I would challenge someone to prove it does. Amano does not think so either
but he did not elaborate why.

I think higher CO2 level can be tolerated and less likely to cause fish
issues if you add the CO2 at high levels a few hours(say 8-9) vs adding the
CO2 at high levels 24/7. If you are off a little bit or the flow rate varies
etc, the 24/7 tank will be worse off. The 8-9 hour dosage has 15-16 hours to
purge the excess CO2 while still getting the same high O2 levels from the
> Thanks,
> shireen
> P.S. I realize I could get an answer if I comb through the
> archives. But I just don't have the time. So if this is a
> question that's been asked a billion times before, please
> forgive me.

Make that a billion and one:-)

Tom Barr

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