Re: Enigma

>> Subject: Enigma
>> I have a 150 gal. heavily planted tank, fertilized with CO2 and PMDD.  =
>> Nitrates are 5-6 ppm, Fe is 0.5 mg/ml, GH =3D 120-130 ppm, Ph is 6.4-6.6, =
>> phosphate level is below 0.1ppm.  The weird thing is every time I do a =
>> water change I suddenly see a burst of activity in my plants, i.e. the =
>> plants release oxygen bubbles like crazy.  This, to me, indicates a =
>> nutrient deficiency but I can't figure out what it could be.   Any =
>> idea's???
> The same thing happened in Kevin's tank, so we tried a couple
>of experiments.  It isn't a shortage of nickel or cobalt.  It now occurs
>to me that one might use up all the calcium in soft water, so we should
>try that too.  If I remember correctly, Kevin tried NaCl, so it isn't
>either of those ions, either.
> The water going into the tank would be expected to have a fair
>bit of dissolved gas, if it came from a cold water main, but I wouldn't
>expect it to be enough to produce the sort of effect Kevin regularly
>saw (and still sees, Kevin?).

I noticed a similar reaction in my tank after large water changes and theorized 
that the large water changes were improving the optical clarity of the water by 
removing large amounts of the "yellowing" substances in the water.  The plants 
were photsynthesizing more because the light intensity had increased 
significantly, especially in the blue region.  This is a common result in reef 
tanks that are given large infrequent water changes or large additions of 
carbon.  The increased amounts of visible and UV light often causes bleaching 
of SPS corals.  An old reef keepers trick is to take a piece of white plastic 
and mark a yellow stripe on it using a yellow marker.  The distance from the 
glass through which the stripe is visible can give a relative measure of the 
amount of yellowing of the water.  Measuring the distance before and after a 
water change would give an indication of the reduction of yellowing in the 
water.  Craig Bingman published several articles on this subject in Aquarium 
Frontiers magazine.  Although it's mostly focused on reef tanks, I think it 
applies here also.