[GpsFrontier]

Hello pineapple,
Where are you located? I'm in Arizona. You said " its hard for me to find all the equipments, materials, references and local experts." So it might help and make a difference to know what challenges you are dealing with in your area.

1. Im using tap water. It's ppm is about 40-50 ppm.

Typically I would not recommend using tap water. But 40-50 ppm is quite low for tap water, and your tap may be OK to use. This may come down to where your located because everyone's tap water is different, but do you know what that 40-50 ppm consist of (iron, calcium, etc.etc..)? Also do you know where your tap water comes from (reclaimed water, well water, stream' river water, etc. etc..) Also are you absolutely sure your readings are correct? Electronic ppm/tds/ even pH meters can easily give you false readings even if their cared for and calibrated correctly.

2. The A B solution i bought is mixed by local retailer themselves. So it has no brand and specification. On the other hand, fertigation system is rising at my place. They have plenty land to plant fruit and vegetable. So i guess, the nutrient they mixed is mainly for fertigation purposes. Im not saying that i got cheated by them. They maybe right and my technique is wrong.

First I don't understand the word "fertigation." It may be because your from a different country or speak a different language, but I cant find a definition for it. However by your reply it sounds like you have a local fertilizer company bottle their own brand of fertilizers for you. This may or may not be a problem. There are many company's that make and sell their own brand of hydroponic fertilizers, however they have to be manufactured specifically for hydroponics. nutrients that are designed for hydroponics also typically contain pH stabilizers.

If their not designed for hydroponics, they will be missing micro-nutrients that are essential for healthy plant growth, and never work for hydroponic applications. Not to mention that nutrients designed for soil often use different type of mineral salts (because it's cheaper and not needed for soil) that not only don't dissolve completely in water, but also bond easier to other mineral salts making it so the plants can't absorb them.

If they are designed for hydroponics, the manufacture should also have a mixing chart so you know how much to add per gallon/liter of water.

3. 28-33 Celcius is air temperature. Sorry i forgot to measure the water temperature.

Water temperature is very important. If it's to high it causes heat stress for the plant. Think of it like being in the desert on a hot day and having all the water you want to drink, but instead of being cool water, all you have to drink is hot water, it wont do anything to cool you down. Just adding to the heat exposure your already experiencing instead. With water temps in the high 80's Fahrenheit or higher the heat stress will begin to cause the plant to go into survival mode. Dropping all fruiting and all other functions, and diverting that energy to just trying to stay alive.

If the nutrient solution is to cold it will stunt the plant growth (slowing down how fast the plant can grow). I just use a $2 glass aquarium thermometer to check my water temps. It's simple, easy, and cheap.

4. I check it once a week. Most of the time, the ph level is quite stable. Im using HI98103 Checker® pH Tester. Never try ph drops test

First I would recommend you check it daily because your new to hydroponics and don't know and aren't used to all the factors that could change your pH. Once your used to them and know the patterns, checking once a week and every nutrient change, as well of when you think there might be a problem would be fine.

5. Yes, i am. About how much air getting to the roots, i dont get you. But the link below is the type of air pump im using now. But this air pump got mention about Air displacement = 3.5L/min. http://www.aquariumtankdecorations.c...efficency.html

I know the question "how much air getting to the roots" is kind of ambiguous because it's not really measurable. The pump your using has a rating of "Air displacement = 3.5L/min," that sounds like it would be fine for the size plants you have going at the moment. But that doesn't mean that that's how much air is getting to the roots because things can obstruct the air flow like a inline check valve, the air stones themselves, kinks in the air line, back pressure of the water itself, and if the pump is even working properly. So you can't really measure the air to the roots. The pump rating is a good place to start, but generally how much air the roots are getting is something you can visually see.

When you look at the water I like to say it should look like boiling water. There are different degrees of boiling water like just simmering, a medium boil, or a heavy roiling boil. For plants your size just simmering should be fine as long as the bubbles are evenly distributed underneath the roots. You want the air bubbles to rise up hitting the roots as much as possible. You don't want all the air bubbles in one spot and the roots somewhere. The roots will absorb dissolved oxygen from the water, but the air bubbles coming in direct contact with the roots is very important also. The direct contact helps keep the roots from suffocating, and the roots absorb other elements from the air like carbon as well.

You can never really get to much air to the roots withough't taking the roots out of the water. Then it's not a mater of getting to much air to the roots, it's a mater of depriving them of water. The bigger the plants get the faster the roots will deplete the dissolved oxygen from the water, so the more air bubbles will be needed to replace it and keep up with what the plants take out. Smaller plants don't need as much, that's why I said that for plants your size just simmering should be fine. But when they get bigger I would want to increase the air to a looking like a medium boil at least.

That's not to say plants won't grow when getting less air to the roots. I have done just that myself growing 8 lettuce plants with a twin output air pump that was broken and only one side was working. The lettuce surprised me how well it did with half of the air bubbles I intended it to have. But at the same time lettuce plants don't mind wet feet as much as other plants and aren't that big. But you can never get to much air to the roots and they would have done a lot better had they gotten more air.

With all that said, I know it's hard to really see air bubbles and water movement as in boiling water in pictures. But I couldn't see any in the pictures you posted. That's why I asked about it even though I could see what looked like an air line going to a air stone.

6. sorry, there is no way for me to measure humidity level.

Even if you don't have a humidity meter, you must have some idea what the humidity is in your area. Here in the desert where I live, the humidity is under 20% most of the year except monsoon season. And in Florida the humidity is very high, especially during summer, reaching almost 100% during summer months there. Humidity is important to plants, even more so when their young because they haven't developed a large root system to suck up the water the loose through transpiration if they have to transpire a lot. If the humidity is low you can put a cover over the plants to create a mini greenhouse environment for them.

7. Im using natural light. I do cover my plant with knitted shade fabric 50%.

If the plants are in direct sunlight I have to wonder if that is adding to the water temperatures. Because even though It looks like the trough and floating raft is made is Styrofoam, and Styrofoam is a great insulator, the raft doesn't look like it covers the water completely.

8. To prevent algae turning my expanded polystyrene raft in to green disgusting raft

Ah, OK, just wondering if the raft was made of something that wasn't waterproof and you were trying to water proof it. My only concern with the black plastic is black absorbs heat. If it begins to get warm from the sun before the plants get bigger and shade it from the sun, I would think about covering the black plastic with a white plastic. If you can find it maybe even replace it with panda plastic. Panda plastic is black on one side to block light, and white on the other side to reflect light and thus heat.

Fyi, those orange/red cubes are plastic sponge. I saw thai farmer using it.

Are the tops of those sponges wet/moist all the time. If they are, that can cause stem rot... you don't want the base of the plant's stem to be in contact with moisture all the time. If it doesn't have time to dry out, it can rot because of the constant moisture.