High Nitrate level

Well its not all that nigh but is n th low end of the stress scale,
next to high borderline. Ammonia and nitrites are 0 ph and alk is
fine.......but I find high nitrate. I did a partial water change the
other day and its still goes right back to the current level. I have
numerous plants, and good filtration. (1/2 barrel setup) All th
plants are doing fine, real nice and green except for the one water l
illy, it seems anemic as it has some nice dark leaves while others are
a pale yellow green color. It was fertilized prior to be put in place
inthe 1/2 barrel, and was fertilized regularlay before that, but it
only ever gets maybe 5 to 7 leaves at most.......The miniature cat
tails are so so, awfull fragile and bend and crimp very easy and not
really all that dark. I use Plant Tabs which is an aquatic plant
fertilizer. Any clues whats wrong on the high level of nitrate and the
water lilly?

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