Hi all,

At last I identified most of my plants

a bunch of Limnophilla sp.
a bunch of Hygrophila difformis
         3 Echinodorus Bleheri (young)
         5 Acorus gramineus var. pusillus
         3 Echinodorus Osiris (young)
a bunch of Hydrocotyle Leucopetala
a bunch of Rotala Wallichii
         3 unable to identified species.

All species doing well except for Limnophilla and Acorus. Acorus is 
worst because it did not even grow new roots. I used to have a lots of 
Limnophila Heterophylla but they all melt and I remove them. The other 
unidentified Limnophilla species was slightly affected before I 
discovered my PH is way too low, going below 5.0 even with 25% water 
change weekly. Quickly did a 50% water change and PH went up to 6.5. 

My question is what can cause the PH keep going down? I have a large 
drift wood. Could this pose a problem?

Tank size is 50gal. with 2 Black Mollies, 4 Zebra Danios, 1 Flying Fox, 
1 Pleco. Filtered by Fluval 303 with ceramic rings, active carbon and 
fluval sponge. 1 Triton, 1 Aquari-Lux and 1 Phillip Super Daylight 
bulbs. Coarse sand gravel and many stones.