First of all, in order for your plant pods to grow in the best possible conditions, your floaters must always have an adequate amount of water.
Here is a picture of the ideal position of the floaters:
Also note that you should never empty the water from your floaters, even if you think it is dirty. In reality, it contains nutrients necessary for the good development of your plant. Simply refill them with tap water, and leave the existing water. Also, remember to keep the light 5cm away from your plants if your light is placed too high, your plants will grow less well.
Regarding harvesting, there are many ways to prune/harvest plants.
But generally speaking:
☞ For bushy plants with nodes (type Basil, Mint, Tarragon, Thyme...): you have to cut the main stem between two nodes. The stem will heal and new stems and leaves will grow from the last node. Avoid tearing off the leaves, it is too traumatic for the plants. Here is a short explanatory video, on how to become a great gardener
☞For plants with stems such as Chives: you have to cut the plant leaving 10 cm of height. The more you cut it, the thicker it will become. The first harvest of the Chive is always the smallest. Here's how to prune it in video
☞ For plants with stems and leaves (such as Parsley, Cilantro, Dill...): harvest the outermost whole stems first, and leave the inner stems to create more stems and leaves around them. Do not pull out only the leaves, it kills the plant. Here is an explanatory video