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Growth problem with aquatic plants
Hi everybody. I' ve gotta question:
For some time now I have encountered problems with the growth
of my aquatic plants. Although the plants do actually grow, the
older leaves of the plants become curled and hard and
sometimes drop off. Especially Lobelia Cardinalis shows these
kind of symptoms but also Ludwigia Repens, Hygrophila Stricta
and Althernanthera Reineckii. The H. Stricta develops small
brown spots on the older leaves which eventually drop off.
I found in the archive of the aquatic plants mailing E-mail list
a table by Neil Frank with nutrient deficiency symptoms and
it looked as if there was a potassium deficiency. So I added
once a week a teaspoon of K2SO4 to my 500 l tank. I also
used Dupla24 fertilizer (10 drops every other day) and 10
drops every other day of my own PMDD based on EDDHA
(sequestrene manufactured by CIBA GEIGY). CO2 is
added to the tank by DIY sugar and yeastmethod.
After adding the K2SO4 some plants really took off
especially Hygrophila Difformis and Hottonia Inflata. But
once again the older leaves became blotchy and ugly.
Large holes appeared in the leaves of Barclaya Longifolia.
Also beard algea and hair algea showed up. IMO it is clear
that the plant are lacking one or more specific nutrients.
Can somebody give me a hint of which nutrient(s)
my plants are missing?
Here are some specifics of my 500 litre aquarium:
pH 6,8 - 7,2
KH 6 dH
Nitrate 12,5 mg/l
temp. 25 C
Fe level (no level detectable with my Dupla testset)
The substrate consist of gravel mixed with sand.
Some loam is added. Also about 10 fertilizertablets are
buried deep in the substrate. The tank is lighted by 2 x
58 W Philips 830 and 2 x 58 W Philips 927 tubes
(max 3 tubes or switched on at the same time).
The ballasts are mounted underneath the tank to provide
some kind of substrate heating.
I am not certain if this is important but about a year ago
I added some zinc-oxide (ZnO) to the water as a treatment
for a blue-green algea outbreak (2 teaspoons).
Could it be that the zinc-oxide has something to do with the
growth problems because it is still in the substrate?
I am looking forward to your respons.
Jan de Reus, Voorburg, The Netherlands