03-05-2020, 05:41 AM
Join Date: Apr 2006
| | Bio-filtration Required?
Here’s a good question sent to me today.
Question: I read your article on nitrogen uptake in aquatic plants. (Note: article is available on my website.) Given that (most) aquatic plants are adept at processing ammonium (ammonia?) and nitrites. Can I conclude that we can over-filter our water with biological filtration? In other words, are we filtering out the very chemicals that plants need? Thank you again.
Answer: Yes. Filtration removes ammonia that plants prefer and replaces them with nitrates, which require more energy for plants to fulfill their nitrogen needs. Moreover, filtration sometimes includes lots of aeration/bubbling which degasses off precious CO2.
Ammonia is taken up by plants more easily than ammonium; in fact, ammonia diffuses freely into the plant. Ammonia (NH3) has no electrical charge, so it easily crosses the lipid membrane barrier of plant cells. Ammonium (NH4+), in contrast, has a positive charge so cells can regulate its uptake—which is a good thing--but that requires some processing. I would conclude from this that ammonia is probably taken up slightly more easily than ammonium by plants.
There’s a Golden Rule here: the uncharged nature of ammonia is part of the reason why it is toxic to plants and fish when it is in excess. Their cells simply cannot regulate its uptake. It diffuses unregulated through the lipid membrane barrier and creates havoc within the cell. The same rule applies to H2S; because it has no charge, cells cannot keep it out.
Moderate water circulation can be useful. It brings nutrients to plant leaves more quickly. It also distributes heat, especially beneficial to large, deep tanks. Organic soil substrates like potting soil are oxygen-hungry first 8 weeks, sometimes making life difficult for plant roots. Circulation of the overlying water helps aerate those soil substrates.
If you have a small tank (1-10 gal) with good submerged plant growth and a moderate fish load, you don't filtration. With a larger tank newly set up with soil and with lots of fish, you might need some filtration to help oxygenate water as well as to remove ammonia.