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Eureka! (I think)
I have repeatedly posted to this list about a hard-to-solve problem in one
of my tanks. Briefly, lesions develop on the leaves of C. wendtii, C.
cordata and Hygrophilla corymbosa, usually near the center of the leaves
and usually about the time that new leaves are reaching full development.
Over time the lesions become more common and the existing lesions become
enlarged. Eventually the leaves take on a corroded look and die.
Following is a rather long narrative leading up to the conclusion that the
problem was caused by my little plecos.
Several years ago I had these symptoms and a few others on a slightly
longer list of plants and I was able to reduce those problems with a
change in lighting and a small dose of magnesium and potassium. It's long
been my expectation that the remaining problems were also caused by a
nutrient deficiency - probably potassium, and probably caused by a severe
imbalance between sodium and potassium in my tap water. I dosed potassium
in the water up to 20 mg/l and I added additional potassium with
fertilizer sticks, roots tabs and other commercial preparations without
any observable effect
The symptoms are limited to plants in only one of my tanks, so I needed a
cause that was unique to that tank. I use the same water in all my tanks
so nothing directly related to the water is unique to the problem tank.
As a result I looked into indirect causes and also thought that the
problem might be caused by a toxicity to something in the tank.
Last year I posted to the list, asking about toxicity to various plastic
parts and Justin Collins replied that some of his friends had problems
when the suction cups on Rio pumps dissolved (odd behavior for a bit of
platic). I filed that idea away until a couple months ago when I checked
the suction cups on my Rio powerhead and found them severely corroded.
I replaced the Rio and waited to see what happened. The tank had a green
water bloom almost immediately. When the green water cleared up I noticed
that both the C. wendtii and C. cordata had taller, healthy looking new
leaves. I hoped then that I finally found the problem, but lesions
appeared on the tall new leaves just a couple days later.
Then last week I posted about pleco damage on an Echinodorus "Rose'" in
the same tank. I started giving the little dwarf clown pleco's parboiled
zucchini (something that in the past I did only occasionally) to keep them
off the E. "Rose'". Sunday in my weekly cleaning and pruning I noticed
not only that there was no new damage to the leaves on the E. "Rose'", but
that new leaves on the C. wendtii and C. cordata were completely
unblemished. I removed most of the older, damaged leaves to make any
changes more readily observable. Happily, all of the new leaves still
remain completely undamaged.
So now, after at least 5 years of trying to find the cause of this
problem, I think I have a culprit -- the cute little clown plecos that
have lived in that tank now for 12 years. What I think is odd is that
I've almost never seen the plecos on any of the plant leaves. They're
usually gnawing away in and around the driftwood. I see them on the
plants so rarely that I actually thought they had an aversion to the
plants. Damage on the E. "Rose'" was recognizable pleco damage and the
first clue I had (OK, I'm slow) that the guys didn't find plants mostly
This seems to solve my problems in this tank with C. wendtii and C.
cordata. The problem with H. corymbosa is very similar and I expect that
damage will disappear as the plants put on new leaves. This probably also
explains very similar symptoms I had on Anubias barteri nana in this tank
several years ago.
The Rio suction cups didn't cause the lesions, but I wonder if they may
have released something as they dissolved that suppressed the growth of
some plants. The C. wendtii and C. cordata changed their height
fairly abruptly when I took the Rio out. Could the change in habit be
caused by a spring-time temperature increase of a few degrees? Whatever
the cause, it looks like the suddenly-taller C. cordata are going to make
me redo my aquascape before I can photograph things for the AGA contest!
in Albuquerque, where it's about as dry as you can imagine and no
significant rains can be expected for another month and a half.