The one in the "kiam chai ang" is doing well. Unfortunately quite a few of the fish has died as my daughters kept stirring the water and catching and releasing the fish.
The one in my aquarium doesnt seems to be doing too good at the moment. Leaves turning yellowy and seems to get thinner. I suspect its due to lack of nitrogen and UV light.
Need the advice of the expert, Lawrence.
No expert here. Just experience gained from making foolish mistakes.
Yellow leaves are a sign of:
1) Lack of light - change your light tube if old, increase the light timer to max 12 hrs/day, or add another tube if you have reached 12 hrs/day
2) Deficiency - see below.
3) Very fast new growth - congratulations, your plants have taken off after a period of dormancy. Young leaves are normally light, yellowish green, appearing at the crown.
There is a possibility of macronutrient deficiency, possibly Nitrogen, Phosphate, magnesium or Iron.
Old leaves turn yellowish, new leaves are smaller, slow growing and often deformed. Eventually plant dies - Nitrogen deficiency.
Old leaves fall off prematurely. All leaves not as dark green as when you first planted them - Phosphorus deficiency.
Old leaves show yellow areas and the tips and edges start to wither - Potassium deficiency.
New leaves show yellow areas and the tips and edges start to wither - Magnesium deficiency.
New leaves grow out yellowish and do not darken in colour - Sulfur deficiency.
New leaves grow and darken, then turn yellow. Leaf blade is yellow, but the leave nerves are green. Most easily observed in fast growing broad leaved plants like Echinodorus. Iron deficiency.
If you think that I'm repeating myself in the signs above, that's because deficiencies are often interrelated and they are really hard to identify for a first timer (like trying to identify the ailment by looking a the tongue like a Chinese sinseh). Mg, K and Fe affect each other, so they are interrelated. Then there is Ca that comes into play when the 3 are met.
Basically, deficiency is seen among people who drive their plants hard by using bright lights, CO2 injection and heavy fertiliser doses without giving sufficient water changes to dilute buildups of single minerals.
In an NPT, you don't use bright lights, and never supplement CO2, so plant's growth rates are slow and thus they can adapt to any deficiency well. Moreover, the topsoil base layer acts like a mineral sump and it generates its own minerals for plant use too, by breaking down food, detritus and dead leaves by bacterial action, into minerals for the plants again.
In most NPT cases, it is lack of light that cause yellowing, followed by owner's anxiety. Plants grow slower, some go into dormancy in an NPT than that in a Hi-tech CO2-enriched tank. Therefore you may be over expecting.
Give time for observation. Start by the simplest to reverse action - Light.
Increase timer, to not more than 12 hours a day. If you are already there, then check that it actually worked 12 hours a day, and didn't get turned on and off. also check that the tube is not old and dim, otherwise, replace. Then increase another light of same power, and drop timer to 8 hours max.
Observe for 2-4 weeks before making any more change.
Old leaves will eventually die. Yellowed leaves seldom recover, so don't fret that you're doing wrong. Instead, look for new growth. If it is growing new leaves, and growing healthy, then, you're on the right track.