Optimising Plant Fertiliser Dosing

The other side of that argument is that it is not good for fish to dose every day. I know that the amount added to the tank in one go is larger when dosing once a week, but the argument is that it better for fish to add things on as few days as possible.

We are now getting into aquatic gardens vs fish tanks with plants 

No Matt...  not daily...  I'm still very much in the process of trying to find that right balance of fertilisers...  Switched back & forth a couple of times between TNC Lite & Complete, and have just very recently settled on the Lite - the reason here being no additional phosphates in the Lite, with me having a high phosphate level in the tank...  Weekly dosing is the target, and dosing less than the recommended amount, but still working on how much that should be...  Until recently, almost all of my plants were root feeders, with the exception of the Amazon Frogbit floaters...  The addition of Bucephalandra and even more recently an Anubias, has changed that slightly...  So, still looking to find that right level of both quantity and frequency...

Really interesting subject and I agree, this part of the chat probably should be moved to a separate thread...  I can see it being an on-going discussion quite easily... 

I was thinking. If you dose liquid carbon, how long does it remain active ? I suppose this would depend on the plant mass and CO2 uptake. Presumably it could be spent in a relatively short time, causing a fluctuation in CO2 levels during the course of the day.

The principal behind CO2 / oxygen in the water is gaseous exchange. At the surface, where the water meets the air, CO2 passes out of the water and into the air. Oxygen goes in the opposite direction and passes from the air to the water. (Actually, it is a balancing act and the concentrations of both CO2 and O2 balance out across the barrier that is the air/water interface. But the normal concentrations of O2 and CO2 in air and water gives the flows I've described above).

Agitating the water surface increases the surface area of the interface therefore speeds up the flows of gas between air and water.

For a tank that has only fish, which produce Co2 and consume O2, you want to get rid of the CO2 and increase the O2 as quickly as possible, so air stones and increasing surface agitation is preferred.

However, for a tank with a lot of plants, the CO2 that the fish generate during the day will be used up by the plants. At night, the plants stop using up CO2 and produce it. This is why I see the pH in my tank drop overnight (when my tank is correctly balanced), because CO2 reduces the pH of the water. (@Sue has posted the technical explanation for this somewhere). So for a tank with a lot of plants, you don't really want to agitate the surface as it is generally better to keep the CO2 in the water for the plants.

The natural fluctuation of CO2 due to light levels changes is unlikely to trigger BBA on its own. It usually takes an external change to do this. That external influence could be a water change (if the level of CO2 in the tank has got very low) or turning CO2 injection on / off or changing the surface agitation regularly, or turning an airstone on / off. There are also other reasons and these may not trigger BBA.

At the moment I don't have enough fish in my tank to produce the CO2 that my plants would like, so the daily pH cycle isn't quite right. My preferred method for getting the right balance is to increase the amount of CO2 produced by fish (more fish!), also because this is more stable. My aim is to have the right balance between fish and plants so that fish produce all the CO2 that the plants need, no more, no less. But I have a lot of juvenile fish in my tank and what I don't want to do is be overstocked when they've all finally grown!

Have you used the community creator yet? You might have to be a bit creative if your stock choices aren't in the database.

I don't know the particular species you've got (except cardinals) but my gut feel is that you're not as heavily stocked as you think.

(Tips on using the cc: volume should be water volume which is typically 90% of the tank volume)

In it's previous setup, my tank balanced nicely at about 70-80% stocked. I suspect that my stock level to balance now would be higher because I've got more plants. But i also have more slower growing plants than previously, so maybe not.

Anyway, the Cc has me on less than 50% stocked, not taking into account the juveniles, so I'm no where near my balance point yet.

@TopCookie Please see http://www.thinkfish.co.uk/article/community-creator for more info on the community creator which Helen was referring to.

Interesting... 

Had all species with one unsurprising exception; the Corydoras Ornatus...  They are roughly the same sort of size as Sterbai...  So, I used Panda Corys in the calculator but doubled the number from x4 to x8...  This gives me the following results based on the actual tank size (as opposed to probable water amount)

Thanks Donna, and will do... 

The major difference is the selection of an external filter on the community creator means you are suddenly allowed 60 % more stocking than normal. Personally i dont think this is realistic and always stick on oversized internal.. allowing me 20% more stocking for having a great filter.... much more realistic.