Thanks for such a quick reply. I would like to answer some of the questions, since I was not specific enough in my first post.
I have had what they call a 60 liter tank for two years. That's how big they say it is. My online convert says that that is about 16 gallons. It is just about the standard size for beginners. And I suppose because of the water here in Beijing, it took an extra long time to cycle it, about 4 months. But I got it cycled and it has been good water for fish and plants for over 1.5 years.
They Ph has never changed over the years. It has remained at a steady 5.5 to 6 for the last two years. Nothing seems to change that.
I looked online and it looks like my plants a kind of anubias; either anubias nana "narrowleaf" or Anubias Coffeefolia. Anubias Coffeefolia (Anubias barteri v. ‘Coffeefolia’)
They are extremely hard to kill and look exotic so I have had these particular plants in the tank for almost four months and all five of the plants have been perfectly healthy. ...until last week, when I changed the gravel, and suddenly, within a week, half of the leaves on all of the plants are turning mushy or develop brown, dry looking edges that move inward until the leaf withers. Last year I had several others of this same kind of plant and they were in the tank for about six months with absolutely no problems until we went home to the States for fives months and had to start over. So I am sure my plants' condition is as a result of the changes from this week.
The light in the tank is a Sunsun brand, 15w, 220v, 15hz white bulb. The tank is also a Sunsun brand. One of the two lights burned out over 1 1/2 years ago. I did not start adding the anudias plants until after the one burned out, and I have never had trouble with plants before, so the remaining one has been suffucient up til now. As for florescent or not, all I know is that when I flick the switch it comes on immediately. So I guess it is NOT florescent.
As for fertilizer, I weekly add a Malaysian brand "Sonye." It has some English and some Chinese on it, so I assume it really IS from Malaysia and not some pirated scam. Also, I always buy from the same people, and I trust them. (The gravel came from a new store where I did not know the people--I know, bad idea).
So here is the full list of the changes, major and minor, that I made:
As for the gravel, I said "dolomite" but I really have no idea what kind it is. The bag it came in does not even have Chinese characters on it.
It look obsidion-ish to me, though--shiny, black. The girls who sold it (and I do mean "girls," perhaps 18 or 20) said that it is very good for plants. (Of course, sometimes if you ask a leading question in Chinese, they will answer with the answer they think you want to hear). Still, if it is some kind of obsidion gravel, it should be very good for plants--right?
I DID rinse the gravel first, but only once. It may not have been enough. Two days ago, I pulled all of the plants out, pinched off the bad leaves, and rinsed the dust off. And you definitely COULD see a thin layer of shiny dust on them. Right now, the leaves that remain all look better than the previous dying ones. But this morning, I see a two or three with small, brown edges developing.
When I was changing the gravel, I took the plants out of the water and laid them on top of the tank for probably a couple of hours. Would that have something to do with it?
Also for a couple of days, the water level was about two inches too low, so the filter was splashing water in. This would have increased the oxygen level significantly. Would too much oxygen for a few days have caused it?
Also, the overall hue of the tank has changed signficantly. The whole reason I got the black gravel was to change the look of the tank. The tank is now significantlly darker because there is no reflection off the much-lighter, light brown gravel. Are the plants getting less light from below now because of that and that is what is causing it? Again, I have one bulb that is burned out. It could easily be replaced.
Also, the driftwood... Because I wanted a more natural look in the tank, I took out the plastic "driftwood" piece and put it two REAL pieces of wood. They stand upright from the bottom to the top and take up about 1/7 or 1/8 of the tank's space. I intend to cut them down by about 1/5, but don't know where the Chinese version of Home Depot is, so I can't find a saw. They ARE rather large right now, and I know real wood changes the water. Still, real wood changes the water SLOWLY, not immediately.
Also, confession time--I added a little of our upright drinking water dispenser's water (you know the large upright kinds with the large upside-down bottles of water like in offices). I needed to top off the tank to get the splashing down, so I added some drinking water so I would not have to wait 24 hours for the chlorine to evaporate out of the tap water (actually after almost four years in Beijing, I still cannot confirm that there actually IS chlorine in our tap water. Nobody drinks it and it does not smell like chlorine). As for the drinking water addition, however, I added only about 1/25 or 1/30 of the overall water. Might that have made a diffence?