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Re: LFS vs APD wisdim

LFS vs APD wisdom

* From: Kirk Melton <triax at bellsouth_net>

Hi all... there is a local fish store near where I live that preaches a lot of stuff regarding plant care. A lot of what they preach is NOT in line with what I have read on the internet and on APD. All of their display tanks (as well as the ones they sell out of) have conventional powerhead driven UGFs, have plenty of surface agitation due to bubbles rising, have compact fluorescent lighting (not against APD wisdom), no gravel supplementations, and NO CO2 injection. The growth is always lush, and well kept. They have a variety of plants growing on rocks and driftwood, as well as amazon swords which constantly bloom, the most beautiful crypt balansae I have seen, a carpet of microswords, some beautiful red melon swords, and many others. And, no, I don't think they are changing out the plants every few weeks. This is an old established tank - but, they just broke it down and re-did it about 6 months ago. I was in the store today and the assistant manager was telling a woman there who could not get plants to grow in her tank to buy an airpump and stone to put aerate the water, which would stimulate plant growth -- the asst. manager has been there for over 8 years now, and this store has been in business for over 20, and the owner preaches the same thing -- UGF and plenty of aeration for plant growth. They DO add Flourish and Flourish Trace & Iron a few times a week to all tanks. Why is this working for them, but it would never work for me? I have to inject CO2 and keep my water surface virtually still to get results. What's the rationale for these suggestions by the LFS? I almost jumped out of my skin when she was telling the customer to do this.

The value of not having a UGF is that, since there is very little circulation of water through the substrate, much of the substrate becomes anaerobic, and bacteria then reduce insoluble ferric compounds (iron with a plus three charge) to soluble ferrous compounds (iron with a plus two charge). This makes iron available to the plant roots.

However, the fish store people are adding Flourish iron several times a week. This is chelated iron which is iron that is kept in solution by being attached to a large organic molecule. It doesn't matter whether this iron is ferrous or ferric. Either way, if chelated, it will be in solution and available to the plants.

The value of the airstone is that it keeps the water in circulation. Movement of the water increases uptake of CO2 (and everything else) by decreasing the thickness of the boundary layer near the leaf surface. If you have a square inch of leaf surface, and the water is not moving, the leaf takes CO2 from the water next to the surface. This layer of water becomes exhausted of CO2, and now CO2 has to diffuse through this exhausted layer (the boundary layer) to get to the plant. The amount of CO2 that the plant gets is INVERSELY proportional to the thickness of the layer that it has to diffuse through. When the water isn't moving, the boundary layer of exhausted water gets quite thick, and the intake of CO2 drops to low levels. If CO2 is not supplemented, it limits growth, and moving the water will greatly increase CO2 uptake by reducing the thickness of the boundary layer. Movement of water, however, can not get CO2 uptake anywhere near as high as it is in a tank with 20 to 30 ppm CO2. But movement helps a lot. Fish circulate water over their gills to keep the boundary layer of O2 exhausted water very thin. If they stop pumping water over their gills, they die from lack of oxygen.

Water movement also helps with nutrient uptake for the same reasons. I remember reading about an experiment where marine biologists attached various species of marine algae (the large "seaweed" types) to a wooden rack and floated the rack in a region of the open sea where nutrient levels were very low. Somewhat to their surprise, they got good growth, which they attributed to the vigorous water movement over the attached seaweeds due to wave action.

In general, water movement helps to compensate for low concentrations of needed nutrients, but, remember, in a tank, the volume of plants is large compared to the volume of water, and the plants can quickly draw nutrients down to levels where water movement doesn't help any more. Suppose that with water movement plants can do fine at a nutrient level of 0.1 milligram per liter, and you have a 100 liter tank. If the plants take up 10 milligrams, then you are down to zero, and water movement won't do a thing for you.

As long as the fish store people keep their micronutrients and macronutrients at reasonable levels and keep algae under control, They should be able to have nice-looking planted tanks.
Paul Krombholz in warm, windy central Mississippi, watching all the weather activity to the north.