Re: Aquatic Plants Digest V2 #116

>From: Cynthia Powers <cyn at metronet_com>
>Date: Fri, 2 Aug 1996 18:39:06 -0500 (CDT)
>Subject: RO water & plants
>- ---------- Forwarded message ----------
>Date: Fri, 02 Aug 1996 21:55:34 -0500 (EST)
>From: DIONIGI MALADORNO <MALADORD%A1%RNISD0 at mr_nut.roche.com>
>Subject: R.O. water and plants
>To: AQUATIC PLANTS <Aquatic-Plants at ActWin_com>
>Is there anyone around with experience on use of RO water and trace element
>supplements in planted tanks? For my planted 180 gal discus (3 regular
>greens and two Tefe greens) tank I am now considering the possibility to see
>if reducing the water conductivity and general hardness levels I can induce
>spawning. I am interested in evaluating the possibility to  try this in the
>community tank, even if I fully realize that it would be much simpler to
>have a separate breeding set-up. The reason is that I would like to observe
>parental fish behavior in a less artificial environment than the standard
>bare bottom tank. The prerequisite however is that there should be a
>rationale for reducing water conductivity without severely depriving the
>plants of the necessary nutrients.
>I am not a chemist, and I will try to do my best in using correct concepts
>and terminology: please do not scream too loud if I am completely off!
>Currently I have in the tank 5 degrees GH and 2 degrees KH with a pH of 6.8:
>from Degen's book "Discus in the community tank" I got a conversion factor
>of 1 GH = ~30 microSiemens, but I am not convinced that this is correct,
>since GH does not account for all the solids dissolved in water. I know for
>example I have also phosphates (1.5 mg/l, slowly but constantly decreasing
>thanks to improved plants uptake), nitrates (2 mg/l), humic acids and God
>knows what else. Therefore, I do not know yet what the conductivity of my
>aquarium water is, but I am estimating that it should be greater than 150
>microS. From the reading done so far, my understanding is that a water
>conductivity in the 80 microSiemens range should be a reasonable target I
>could aim at for spawning wild discus.

Niether GH testing nor a conductivity meter "account for all the
solids...". Plants need about 3 degress of KH and 3 degress of GH. You can
induce fish to spawn by adding RO or DI water at a temperature lower than
they are used to (think of a rainstorm), but the lowered hardness need only
be provided until the eggs are fertilized.

>Here are some thoughts on which I am interested in hearing comments that
>might help me to understand the feasibility of this project:
>1) I know my tapwater alone does not provide sufficient nutrients for the
>plants, and I guess that PMDD supplementation of RO water (possibly buffered
>a little with sodium bicarbonate to maintain 1-2 KH degrees) should still
>provide adequate nutrients to them. If this is not the case, a nutrient
>deficiency should occur gradually, and monitoring of the plant conditions
>and return to the current water change procedures should prevent
>irreversible crashes in the plant population.

You need to reconstitute RO water, ie: add trace minerals. Bicarb alone is
insuffieient. Iron is the most important metal for plants. I use bicarb to
bring up KH only if GH is sufficient, otherwise I use a commercial recon

I suggest a KH of at least 3.

>2) does anyone know what is the conductivity of deionized water supplemented
>with the recommended PMDD doses (1 ml/10 liters, if I remember well)? My
>whole idea depends on whether or not I can use adequate PMDD amounts with RO
>water, staying below ~80 microSiemens. As soon as I receive the tester and
>the RO equipment I will of course be able to estimate that by myself.

RO units will produce water with varying degrees of hardness, depending on
water line pressure, water content and other factors. Think of RO as a very
fine mesh filter. DI water (such as produced with the Aquarium Pharm. Inc.
TWP) can be reconstituted "by recipe" because it is pure water, but I do
not believe that RO water can be. (ie: you have to test RO).

I used to have angels that spawned every time I did a 20% water change with
pure DI water at room temp.

Plants can take the reduced hardness for a short period of time. In a
general sense, plants need hardness mainly in order to grow. (same for
fish). You are right, however, in noting that a reduced KH will eventually
cause a plant "crash", especially in the presence of high nitrates. It
happened to me big time.


-Bill Brady