I like Flowgrow plant database. In fact, I consider it the best on-line database in Europe. Above all, I appreciate it's botanical accuracy.
I'd like to believe that the database has been created by people who have got many opportunities to keep described plants and know a lot on their demands.
In theory, pH may be influenced by many factors. In practice, though, there's only one - alkalinity. Nitrification pushes pH down by consuming alkalinity (bicarbonates). Plants' photosynthesis pushes pH up thanks to carbon dioxide uptake. Humic substances? They're not bicarbonates, of course, yet they too affect alkalinity, and pH accordingly.
The only commonly used way to decrease pH while not affecting alkalinity is carbon dioxide injection. I don't do it but I understand that many hobbyists do. What is the maximum level of CO2 which can be considered rational? 40 mg/L, perhaps?
Ok. So, CO2 content may vary between 0.4 mg/L - based on partial pressure of CO2 within air - and 40 mg/L. I believe that the people who contribute to the database keep CO2 content within this range. And that they've got personal experience with those plants for which they provide guidelines.
And then - I can see that their recommended values are completely distracted from reality. Let's look again at the example (only one from many similar ones) mentioned above: If I choose MEDIAN values, i.e. pH=6 and alkalinity 7 °dKH, it returns CO2 content 246 mg/L. Is this a joke? In fact, you can combine the suggested numbers in any way you choose, and you get rather fair numbers solely for pH=7.
So, can I TRUST these guidelines? Do the authors truly speak out of their experience? Or are they just suggesting random numbers without much thinking?
You say, use your own wits. Fair enough. But what are these guidelines good for, then? Wouldn't it be better to cancel them completely? Or - that's my suggestion - to cancel data on alkalinity? In my experience, pH is the parameter which truly matters.
I still want to trust this database. I still want to believe that there are people who know and are willing to share their knowledge. It must have been a lot of effort to create and maintain the database. It deserves to be corrected not to speak nonsense.
Imho these low values have no practical relevance. I can add salt to have a calculated value in that range, but I must ensure the salt is equally mixed and hasn´t adsorbed any water. But most salts are hygroscopic and so on ^^ It´s quite a mess to ensure these values.
