By Tom Barr
I found that adding lots of fish and plant filters to a fish-only tank that was fed well did great as there was no ammonia or nitrates and explosive growth on several plants. I did not add any trace or macro supplements, just fish food and the fish.For example, a growth rate of 3 to 6 inch daily vine growth on a Clematis. Peace lilies(Spathiphyllum sp.) do very well and require very little light (often you are able to get away with ambient light only).
No need for CO2 and lots of light yet you get the benefits of plant filtration. Not bad for a fish only set up, eh? I had a 100 gallon with about 400 inches of fish in it and 4 such tubes. No ammonia in my tanks or NO3 that I could detect but that was some years ago with a Tetra kit. Fish did great though and I never had to clean my filter unlike my old method. I just hacked back the plants instead. This got me into submersed plant more and more and more.
I used a simple sump with 3 inch PVC tubes filled with lava about 14 inches tall. In these tubes I added several types of plants like you would if they were being potted in dirt. The sump water level was/is about 5-6 inches deep. The incoming water trickles over the plant's roots in a slow wet/dry fashion and exits out the bottom. I added a 15-watt light under the sink type FL ($6.00) and let the vines crawl out the back of the stand all over the back of the tank were it could get some window light. I used test caps to seal off the bottom and drilled small holes for drainage. These plants will show signs of deficiency just like submersed plants but to a lesser degree (it won't be from lack of CO2) and the bacteria in the wet/dry tube will keep filtering also... the best of both worlds IMO.In this manner you can figure out your fertilizer regime without losing any filtering capacity because the bacteria are still there but you need to get the nutritional requirements up for the plants. It can act like a safety net say if your CO2 runs out etc.
The main reason my plants did bad was when I removed all the fish and stopped feeding them. They perked right up when I added the fish back and did some over feeding. I liked fish more than plants then so the plants was the "leftover food eater" basically. It's about balance. The bacteria will find a niche no matter what but the plants can suffer if things are out of whack.
lant filters are nice if due to the aerial and light advantage. Your submersed plants will suffer if the CO2 is not doing well but they will suffer anyway if you don't add any(CO2) so there really is not this competition between plants or the bacteria. Bacteria don't need light (most). Removing the filter and using a powerhead only, will increase the the growth often (more NH4+) but it depends on how your tank is maintained and balanced not the issue of competition (a balance of 25% NH4+ and 75% of NO3- is sometimes referred to as the best range in hydroponics set ups). I wouldn't try this ratio in a planted tank water column but it can give some insight into different Nitrogen sources for good growth.
This same set up can be used as a hang on plant filter also by adding an "L" PVC to the 3-inch tube about 5 inches up from the bottom and hands from this "L". A small powerhead can supply the water or be split among several filters, RFUG's, tank circulation etc.
Balance, not competition, is the general idea. How you balance things depends on you. I think plants and bacteria are friends generally unless you try really hard to make them fight!
Bacteria have been around far longer than plants and they have evolved with bacteria. Each has their own niche. How we make the conditions for these niches is another issue. I have used these filters on many tanks over the years and they work well with a planted submersed tank and with a fish-only tank.
Some submersed purists may feel that an aerial plant is competition for the submersed plants but it goes back to how you balance you tank. You could add more submersed plants to your tank also. The resulting depletion will be the same but the CO2 and light will be more consistent for the aerial plant adding some stability. Submersed only control of nutrients is a nice goal and this method is not challenging this concept but is merely adding another option to planted tanks.
Plant filters are likely the first of all the filters for fish tanks/ponds dating quite far back into the 1890's or so. This is not a new idea by any means. Hydrologix also sells these plant filters and are on the web.