re: Calcium and aquatic plants

---------- Forwarded message ----------
> From: spush at saudan_hac.com
> Message-Id: <9612060037.AA02399@sawgrass.hac.com>
> Subject: Re: Calcium and aquatic plants
> To: Aquatic-Plants at ActWin_com
> Date: Thu, 05 Dec 1996 16:37:02 PST
> In-Reply-To: <199612050839.DAA11517 at looney_actwin.com>; from "Aquatic-Plants-Owner at ActWin_com" at Dec 05, 96 3:39 am
> X-Mailer: Elm [revision: 109.14]
> In the Dec 4 edition of the APD Dave Huebert questions the accuracy and
> usefulness of a table quoting average nutrient content of plants and
> aquarium water and in particular the statistics pertaining to calcium. 
> I'm glad you raised these points Dave. Of course the data are not from 
> scientific literature but from the Feb, 1988 "Today's Aquarium, the 
> International Magazine of the Optimum Aquarium", ("Aquarium Heute" in 
> German) which perhaps illustrates a good point; just because something is 
> written up in a magazine or "authoritative" reference book, doesn't mean 
> that the subject material is without errors! If anyone has this issue
> of Aquarium Heute, perhaps they might check the article for bibliographical
> notes. (George?)
> Dave also questioned the usefulness of an average Ca concentration
> in plant tissue. I'm not sure if I understand the issue completely but
> let me bring the discussion back into focus by re-stating the goal.
> My purpose in seeking the mean concentration of nutrients in plants is to
> help us develop an educated guess as to an appropriate dosage, relative to
> other consumable nutrients that will give us an acceptable steady state
> concentration of Ca in our aquarium water. As with phosphorus and some other
> nutrients, it is clear that an extremely wide range of concentrations is
> acceptable for growth. In order to predict the amount of Ca we need to
> input into the system in order to maintain a reasonable equilibrium
> (and I think we agree that the guess need not be precise since the range
> of acceptable steady state concentrations is fairly wide) we need to look 
> at how much Ca will be consumed by plant tissue growth. The dosage should
> probably be conservative so that the hardness of the tank water does not
> tend to increase with time. Periodically, one may apply a single larger
> dose to bring the hardness up to the desired level. The problem with
> measuring hardness is that it is so easily affected by other minerals
> esp. Magnesium which we're adding in a fairly high dose with PMDD.
> Referring again to the average nutrient content of plants, the ratio
> of N to Mg given is 3,200 mg/kg to 210 mg/kg or 15:1.
> To say that sufficient Ca will be supplied by either fish food or by
> water changes doesn't seem to be the case for me. I'm adding small doses
> of limed water and over the course of three months, the improvement in growth
> seems to be established. Certainly other factors _could_ be affecting it
> however I suspect it was indeed Ca deficiency since these symptoms
> tend to be associated with either Ca or N deficiency. N is not deficient.
> In my situation, I'm not sure I can produce a reliable ratio of Ca to
> N for dosing since my tanks are being supplied with N either from the
> recent soil substrate or in the other tank from feeding of a relatively
> large population of fish.
> I'm also unsure that I could establish a reasonable Ca dosage for my tank 
> since the CEC capacity of my substrate will probably act as a _damping_ 
> _factor_ for Ca. Ca ions readily displace other cations from cation 
> exchange sites. Incidentally, this in itself can produce improvements in
> growth by liberating NH4+, K+ as well as trace elements like Fe, Cu,
> Mn & Bo. To perform an accurate experiment one would need to use either
> soil-less plants or measure the Ca concent of the soil before and after
> the experiment. Using less than a "typical" mixture of aquarium plants
> defeats the purpose since those floating plants may have a different
> Ca budget. Measuring Ca content in soil is perhaps a little tricky.
> Again, let me refer this question to the various experts in each field.
> How do we best establish a reasonable Ca dosage? Should it be calculated
> relative to the nitrate dose in the PMDD? Or empirically determined
> by measurements over a long period of time by measuring general hardness?
> Steve Pushak      spush at hcsd_hac.com       Vancouver BC Canada