Effects of high temperature on plants

[leebc at sbs_sumibe.co.jp]

Hello,

I am curious about the effects of high temperatures on the plants.  The
water in my tank usually stays at 27°C to 30°C (81°F to 86°F).  I have the
following plants.

Alternanthera reineckii (growing but not doing so well)
Eleocharis parvulus(turning to dark color... almost blackish)
Echinodorus "ozelot" (just planted)
Echinodorus tenellus (good growth)
Hygrophila "Stricta" (good growth... but very prone to have small brown
spots despite regular K dosage)
Hygrophila deformis (growing rather leggy despite being place at the
brightest spot)
Hydrocotyle leucocephala (ok but not spectacular)
Lobelia cardinalis (just planted)
Nymphea ?? (growing very well)
Vallisneria spiralis (ok but growing in spurts)

My tank:
60L (16 gal)
36W CF + 15W FL
GH 6-8
KH 4-5
pH 6.5-7

I wonder if any of the above symptoms are due to high temperature.

Thanks in advance for any advice.

BC (Singapore)