Daniel Morrow at was heard opining:

Nitrite is
borderline and nitrate is way too high.

The hornwart should have taken care of nitrates. It sounds like your tank
needs a lot of partial water changes and some good gravel vaccing.

Every other parameter is fine
except for maybe the ph being at 6.5.

I found keeping guppies alive and healthy takes water with a PH over 7.
They do much better in harder more alkaline water. In a PH below 7.2 an in
slightly acid water they don't do nearly as well. Anyway, that's been my
experience with guppies and other live bearers.

Ripping out the hornwort should
cause more to grow and thus more nitrate to be removed in the
process.

That can happen! :-) I'm surprised it's growing so well for you as it
didn't thrive for me in NY's soft slightly acid water. I just had an odd
thing happen with hornwart. After having it for many years, both indoors
and in my ponds - about 90% of it suddenly did a die-off! I once read about
bamboo doing the same thing. I suppose it'll spring back from the small
bits I have left of it....... if not I'll have to start with a fresh bunch.

Thanks again - good luck and later!
--
Koi-Lo.... frugal ponding since 1995...
Aquariums since 1952
My Pond & Aquarium Pages:
http://tinyurl.com/9do58
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