You might get a tiny amount of refraction but it should only really refract towards the tank and plants.
In order for aquatic plants to survive they need to be able to a) be truly aquatic plants and not semi aquatic (there are a few plants sold as aquarium plants that are not) b) have access to nutrients either from the substrate or water column (preferably both) c) take in enough available carbon to grow d) be under sufficient lighting to carry out photosynthesis.
Nutrients: plants need certain nutrients in certain quantities in order to survive. In larger quantities they need nitrogen (N) phosphorous (P) and potassium (K
) you may hear of these referred to as NPK or macronutrients. I would also class magnesium as a macronutrient too. Then they need all the other nutrients that are required in small quantities known as micronutrients. Things like iron, copper, boron, manganese, zinc.
You can buy macros and micros as dry powders or 'salts' and mix them yourself to save money. You can use a substrate like Eco complete, ADA aquasoil, garden topsoil or flourite although these may not contain everything the plants need. Fish food and water changes may also provide some nutrients.
Carbon: probably the most important nutrient for plant survival and the main reason people fail or have failed in the past like myself. The availability of carbon to aquatic plants is extremely limiting. It diffuses through water extremely slowly and always wants to reach the surface where it can enter the atmosphere and plants normally cannot fix enough carbon in order to survive. The higher the light intensity the more carbon and nutrients are required. If you have strong lighting and do not supplement carbon either by liquid or gas the plants will die. When plants die algae follows. If you have low intensity lighting then you may be able to grow a select number of plants that are suitable under these conditions know as 'low light' plants. Lower light conditions and lower light plants require less carbon and simply keeping the water Column in equilibrium with atmosphere by allowing good surface agitation or by using a tank with a higher surface area to volume ratio is enough to keep plants alive. Having harder water may also help as plants may be able to use the carbon in the form of carbonates to grow.
Light: plants need light that falls between 400nm and 700nm. Light in this range is visible light and is known as photosynthetically active radiation or PAR. You will hear of light intensity be referred to as PAR. The higher the PAR the more photons are able to reach the lower part of the aquarium conversely a shallow aquarium with a lower PAR may have the same PAR at substrate level. PAR will always be greater closer to the light. The more PAR the more need for carbon and nutrients.
Beginners are recommended to start with low light plants that don't require carbon supplementation which require less nutrients.
There are plenty of threads on here that list lower light plants and will help you to set up lower light aquariums. Remember though that low light doesn't mean no carbon. People still supplement carbon and use lower PAR for ease of maintenance as higher PAR also means faster rates of growth IF carbon and nutrient requirements are also met.
Any questions feel free. Hope this helps.
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