Things Beginners worry about but they shouldn't

When you are new to growing plants (in any way, not only in Hydro) you tend to worry about things that are really not important or unavoidable. There is nothing like a perfect specimen in nature. Go out and find a tree. It has all kinds of imperfectness on it, yet it is completely healthy. Plant time is not the same as human time. Think in seasons and years, most of the plants show results only in the next year's growth period.

Foliage

When you google a plant's name, all the pics show perfect leaves. No brown tips, or misshapen ones.

Every grower has experienced the panic when they see something unusual happening to their precious'. As dry air is very common especially in the heating season, a few brown tips are unavoidable. A Calathea won't ever look the same in your living room as it would look in the jungle. Accept this. You can raise humidity in your home but that is probably an endless fight.

Misshapen leaves occur naturally. Remove them, but when there is more than just a few, there must be an underlying problem of illness or lack of nutrients.

A few fallen leaves don't mean your plant is sick, especially when it has a hundred other. It happens when you bring them inside at the end of Summer, when temperature drops within a few days or you just repotted them. Give them time to adjust. 

Light

Choose a spot for your plant and leave it there. Most of them don't appreciate changes in amount and direction of sunlight. Keep them out of scorching sun and away from dark corners and they will do fine. Many plants get sunburnt if put outside in summer without enough time the adjust. First keep them in bright shade and week by week introduce them to full sun. Many of them will be grateful and gift you with nicely coloured leaves and vigorous growth.

Don't use ordinary bulbs as additional light, it's just a waste of energy. Common houseplants do well in lower light conditions during Winter months.When Summer comes, snip the etiolated parts off, and fix the look.

Grow, please!
There can be numerous reasons why your plant is not growing beyond you do something wrong. Maybe it is only a slow grower. Many houseplants put out only a few leaves per year, researching your precious' habits helps you understanding it better.
Check the roots. The pot may be overcrowded. It is very easy to repot when growing in Hydro, so trim the roots and if necessary you can go for a bigger pot.
Feed them well. Some research is necessary, even when growing in Hydro, some plants don't need as much mutrients as others. Adjust the amount of fertilizer given to help them reach their potential.
Sometimes, to see nice growth, you need to cut first. A smart trimming here and there encourages branching.

Water
It is the most common thing plant owners worry about. People tend to think when a plant is sad-looking, it needs more water - which is completely wrong (this we know since we grow in semi-hydro). If you are aware of the needs of the plant, and understand the signs of stress, you simply can't go wrong.

Feeding
Feed your houseplant regularly, but only with an appropriate fertilizer and always follow the instructions. If you fertilize too much, roots can burn and your plant would look just as sick as it was in need of nutrients.

Plants I killed

As growing houseplants in semi-hydro is an experiment and there are tons of things I don't know or understand yet, I managed to kill quite a few plants. But I've learnt from my mistakes every time.

One plant that died on me was a Calathea albertii. It was a salvaged plant from clearence shelf. After repotting it bounced back nicely but then started losing old leaves. However, new shoots sprouted. The plant lived for a good 3 months but kept dying back. I couldn't seem to find the reason why. Then noticed tiny white and black powdery things on the back of the leaves that didn't respond to any treatment I tried so had to get rid of the poor thing before the didease spread to other plants..
Calatheas can be finicky. I am having problems with a zebrina and a roseoptica at the moment (maybe dry air due to heating, will try to bag them for the rest of the season).

Another loss is a Haworthia pentagona that collapsed a few days after I transplanted it. Maybe got too wet while I removed the soil from the roots. It never seemed to mind the showers though.

I learned that ferns don't especially like direct sun and semi-hydro. I am lucky with my Asplenium nidus as it is doing fine but not as lucky with Polystichum tsus-simense aka Korean rock fern. It simply dried out beyond saving in a few days time on the windowsill. I was too careless I believe.

The mango I grew from seed got a bad thrips infestation. The avocado seeds didn't even sprout, maybe it's best to root them in water

I don't know anyone who hasn't killed a plant yet - by accident, by carelessness, by incompetency or other reasons. So don't be sad if you fail once or twice, next time you will be more careful.