Undersized canister filter better for plants?
I have a new 55gal tank (running three weeks now). I'm using a borrowed Eheim canister filter, the smallest one, that's rated for 35 gallon tank max. I planted a the tank with several large swords, cabomba, and a variety of other plants using ecocomplete substrate 2-4". I have a rather mixed crew of fish cycling the tank (18 fish total, guppies, danios, and 5 corys). Although I'm feeding the fish 3-5 times/day and not being particularly careful with the food volume(!) the water quality is excellent, from a fish standpoint, 0 nitrates/nitrites, no detectable ammonia. I was planning to purchase an Eheim classic soon, but since the tank parameters are doing so well, is the undersize filter actually going to work out better? It's my (plant newbie) understanding that less water flow/surface agitation is better. Right now I have a 24" dual T5HO on one side of the tank (all plants are on this side). I'm not planning on messing with any CO2 and the plants, so far, seem to be doing well. For plants, IS a smaller canister actually an advantage?
To start off first--welcome to Tropical Fish Keeping forum.:wave:
As you correctly mention, it is the water flow (current) and surface disturbance that is the principle concern with filtration. But also there is the issue of biological filtration, and I'll start with that.
Plants do a tremendous job of filtration, and in a truly balanced system (meaning minimal or moderate fish load and thick plants) can handle the filtration task on their own. However, water movement is important for the reasons I'll get to in a moment, so a filter won't hurt. It should however be primarily mechanical--removing suspended particulate matter with media, pads, floss, etc.--and not be primarily biological (encouraging nitrifying bacteria) and never chemical (carbon, and similar media that affects the water chemistry by removing non-visible substances). The reason to limit biological filtration is because plants primarily use ammonium as their preferred source of nitrogen--not primarily nitrate as many still write--and they compete with and actually out-compete nitrosomonas bacteria for the ammonia. Plants can also use nitrite and nitrate, in varying amounts depending upon the plant species and other conditions, but they show a marked preference for ammonium. [In acidic water, the ammonia produced by fish and biological processes automatically changes to ammonium; in basic water the plants can use the ammonia and convert it to ammonium.] Nitrifying bacteria in a well-planted and biologically stable aquarium will be significantly fewer in number than in the same aquarium without plants, simply because the plants grab the ammonia/ammonium faster. Since there are fewer nitrosomonas bacteria consuming ammonia, they are producing less nitrite, so there will be fewer nitrospira bacteria to use the nitrite to produce nitrate; as you may know, nitrifying bacteria in any aquarium will be present at numbers sufficient to handle the available ammonia/nitrite and no more or no less under normal stable conditions. This is why nitrate levels are low in well-planted balanced aquaria, even frequently to the point of being near zero on test kits.
Water movement is important for two reasons: removing the minute particulate matter so it doesn't settle on plant leaves (which can "suffocate" the respiration process) and bringing nutrients in the water column to the plant roots (and sometimes leaves). While there is some difference of opinion among the authorities as to how critical this is, most maintain that excessive water movement hinders the second task, bring nutrients to the plants. This involves mineral nutrients primarily assimilated through the roots, and of special significance the assimilation of carbon as CO2 through the leaves. Aquatic plants take four times as long to assimilate CO2 as terrestrial plants, and if the CO2 is being pushed past the leaves too fast it can result in insufficient carbon being available. This ties in with the surface disturbance aspect.
Surface disturbance causes a higher exchange of gasses: CO2 is driven out of the water and more oxygen is brought in. This is detrimental to plants in two ways. First, it reduces the CO2, and as noted above the faster water movement is already reducing the assimilation of CO2 which is now being driven out of the water, totally removing it. Second, an increase in oxygen is known to be detrimental to aquatic plant growth. Oxygen binds with minerals, iron is one but there are several others, making then too large for the plants to assimilate. The result is a deficiency of iron and other minerals, all due to the increase in oxygen.
Now we turn to the filter itself, in light of the above. Water movement through the aquarium is a good thing, but it should be minimal. [The only exception is if there are fish requiring higher water movement, such as some catfish, many of the loaches, etc., that occur in faster streams. I won't go further into this here, except to say that there are compromises in larger (4-foot length) tanks, if this is an issue with the selection of fishes.] In tanks under 55g I myself always use sponge filters; they perform the mechanical filtration excellently, and they provide minimal or slow water movement. For larger tanks, a canister filter works best. I use the size rated for the tank simply because I like lots of fish, and with a tendency toward higher fish loads than what anyone could term minimal, I like to be on the safe side. My nitrate readings bear this out; I have less than 5ppm in the tanks with fewer fish than I do in the more heavily-stocked tanks where nitrate is 5-10 ppm [never higher though]. This I believe is related to the nitrifying bacteria levels I mentioned previously--the more fish, the more ammonia so the more opportunity for more bacteria.
You mention 18 fish presently in the tank; assuming these are relatively small (at maturity) such as corys, tetra, etc., this is certainly minimal stocking, but also assuming that you intend to increase the fish load, you may want to move up to a canister rated to the 55g. This is really up to you.
Thanks for the exceptionally detailed info! I'll probably (eventually) purchase a larger canister just for the flexibility, although I tend to underload my tanks.
Sorry to hijack an old thread, but his applies exactly to what I am trying to figure out right now in one of my 5 tanks.
3 of my 5 tanks are true "Walstad" aquariums - no filter, just a powerhead and loads of plants. The one that has perplexed me is my 55g. I originally planted it with flourite and eco-complete underneath gravel. It was my first planted tank. When things started to go bad, I moved to the high tech approach - T5HO light, injected CO2, etc. The plants were great and I enjoyed that for a while, but I got tired of needing to trim the plants twice a week to keep it from being a jungle.
I took out the CO2, moved down to about 1wpg of T5NO light and a moderate dosing schedule. Algae was under control, but I still haven't been able to keep nitrates under control without water changes. I getting ready to double down again on plant load, but nitrates still escalate - up to 40 in many cases before a water change. The right answer, as I see it, is to go truly low tech with a soil substrate underlayer, but I just don't want to break the whole thing down to make that happen. That's when I stumbled on info about filters and their effect on planted tanks through the internet and Diana Walstad's book.
So my question is this - I am still running a Fluval 305 and a 405 on the tank. Your discussion about water movement was awesome and a lot of food for thought. I am thinking of taking all of the bio balls out of the canister filters and just putting mechanical filtration in there. Obviously "mechanical" filtration will still also act as a biofilter, but I am thinking there will be a lot less nitrification without the bio balls encouraging oxygenation/nitrification. I am even wondering if I could cut back to one canister filter, but I am not sure I could do that without some serious low flow zones in a planted jungle. What do you think?
Max, welcome to Tropical Fish Keeping forum. Rather than moving your post to a new thread, I'm going to keep it in this old one since it saves me having to repeat what I wrote in post #2.:-)
I detailed the reason for minimal biological filtration, so that answers part of your question. At this point I will briefly comment on filters in general. You mention having two filters on a 55g--why? There is no advantage to multiple filters. Provided any aquarium is filtered according to the needs, it is as good as it can get. More filters may actually be detrimental, for reasons I won't go into here. But a canister filter rated for the tank size is sufficient and unless the tank is way overstocked, the best situation. And with overstocking, the answer is not more filters but more water changes. So my first suggestion is to use one filter rated to the tank. Canisters work best on larger (50g and up) planted tanks.
Water flow depends solely upon the needs of the fish species. Obviously it is possible to have a healthy planted tank with no filter at all. Ms. Walstad writes of this, and for decades before we had all the gadgetry we now have aquarists maintained planted tanks with no lights, no heaters and no filters, and the fish were healthy. But there is nothing wrong with utilizing a good filter, and I, like Diana, have one on my planted tanks. The rate of flow must be geared to the needs of the fish; forest fish usually need minimal water movement, while some fish from fast-flowing rivers need a good current. One important aspect of building a successful community aquarium is ensuring the water flow requirements of all fish in the tank are compatible.
Nitrates in a natural (low-tech) planted tank should never be above 10ppm, and most often near-zero. All of my tanks run < 5ppm. If nitrates are higher, it means something is out of balance, or they are being introduced via tap water. But a balanced natural well-planted tank should have near-zero nitrates.
Soil substrates are not the answer. I believe they are highly over-rated. Any substrate will function biologically in a planted tank. My plain gravel and sand substrate tanks have run for more than 15 years, and I have a lot of fish in them.
You might find this article on bacteria helpful:
and thee is also the 4-part series "A Basic Approach to the Natural Planted Aquarium" stickied at the head of this section that summarizes the entire approach I follow. And I'd be happy to discuss further.
Thanks, Byron. I typically don't like to hijack old threads, but this one fit what I wanted to discuss perfectly.
Regarding soil, I have read Ms. Walstad's book and I post on a forum where she is one of the moderators. Her book states you need a soil under layer and she told me that directly in a post a while back - even saying that soil and gravel are not the same thing. I agree that the chemical/biological processes can be different in soil vs. gravel vs. flourite, but I come down more on your side and keep pressing on with this tank.
Why 2 filters? No other reason than I set it up that way quite some time ago! I am going to experiment with shutting one of them off. As I stated, with all of the plants in the tank, I was concerned about introducing dead spots, but I see your point of not need 700+ gallons per hour going through 2 Fluval filters. I have the output on them turned way down, so it's not like there is a vortex in there, but I agree it is probably overkill.
No one has more respect for Ms. Walstad than I do--I have her book, her articles, and am a member of her forum--but there are several methods for a successful planted tank and using soil is only one of these. My tanks certainly disprove her statement that one cannot have a successful planted tank with plain gravel or sand. And there are some problems with soil that have to be managed, and I am not aware of any substantial benefit of soil over other methods.
I agree that soil tanks have benefits and drawbacks... but I'm not absolutely certain that the bacteria works the same in both.
The only reason, is that soil inevitably goes anaerobic in a few spots... And as long as it's kept limited to a few spots, it has the benefit of converting nitrate to nitrogen gas (where it then bubbles out of the system, helping keep nitrates low without the need for water changes).
On the filters- don't worry about 'dead spots' and feel free to cut one off.
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