Re: [RML] Water quality

H. Hoekstra (hugo at
Tue, 17 Aug 1999 17:45:53 +0100

On 17-Aug-99, Ed wrote:

>Regarding water quality testing, assuming that we are taking about
>an established fish tank, with a good gravel bed, water flow,
>in a location with slightly alkaline water supply,
>as most are; imho I think that the best indicator for
>the interval required for gravel vacuuming and water change is:
>nitrate concentration.

>Unfortunately the nitrate test does not seem to be available in
>convenient "dip stick" or continuous monitoring sensor/probe.
>Nevertheless there are practical and economical "manual" nitrate test kits
>in aquarium stores.

>After learning how to test for nitrate I have been amazed at how
>far off my intuition regarding water quality has been. Let face it many
>of us end up with tanks that are overloaded with fish. These tanks

>require more frequent water changes. There is also the wide misconception
>of plants "removing nitrate". While it is true that in nature there are
>definite examples of wetlands with aerobic-anerobic-carbon cycle nitrate
>I have not seen any fish tank that comes even close to nitrate closed
>bio cycle, the only practical approach is the true and tried:
>regular water chance and gravel vacuum.

>Once the volume and time between water changes is established
>continual water monitoring is no longer necessary, for years!

Hello Ed,

Aquatic plants do use nitrate, this is no misconception but scientific fact.
They prefer ammonia as this is more readily available to them though. I have
had {overstocked but} densely planted tanks that are 'nitrated closed bio
cycles'. This doesn't mean that you can stop changing water, only the purpose
changes, you're not lowering nitrates but replenishing trace elements for the
plants. Note that plants can only effectively use nitrate if sufficient
lighting, CO2 and trace elements are available.

BTW the gravel shouldn't be vacuumed in planted tanks, just the debris lying
on top. And I do have tanks which haven't even got any crud build up at all.

Best regards,