Hi Katie,
Its my opinion that one of the first and toughest decisions you have to make about a filter is what flow rate you're going to go for. When I first came here it was a shock to find out that many filters that claim to handle a certain size of tank are really felt to be not adequate by the enthusiasts here. Come to find out, the manufacturers will often have two separate specifications listed on their filter, one that say what size tank the consider it to handle and a different one that says what the flow rate is. The most common advice I found here on TFF was that 5x turnover was the recommended number, more or less the minimum recommended. That's the system turnover, so for your 200g you'd need to turn over 1000 gallons per hour. In practice of course, the manufacturers push the way the numbers are given to the limit, so a published flow rate is going to be a bit of an exaggeration and you'd want your numbers showing above a 1000 even to be really getting the 1000 if that makes sense. Note that most hardware is going to be quoted in liters per hour, so 1000 US gallons is a huge flow rate.
But the worst is yet to come. I later came to realize that the 5x turnover guideline was mostly given out for the fish side of things and come to find out, the planted tank members are quite the renegades and hardly blink at having 10x turnover! Now that's practically a separate hobby, to be as focused on the plants as that, but I thought I'd throw it out there so you and David wouldn't feel like you'd never been told. The advantage they are looking for with all that flow is to not allow any tiny dead pockets that don't have water movement, which would allow slighly higher (still not measurable by our kits, but nonetheless slightly higher) ammonia levels to occur at those spots, which would promote algae and would allow excess food to settle, also promoting elevated ammonia spots. Now, to put this in perspective, remember that these are the extremes of fancy planted tanks, so if you are looking to mostly the tropical fish side of things and don't want to explore this other side of things then its your choice not to worry about those high numbers.
OK, so that takes care of flow rate. Next up is media volume. Regardless of flow rate, every filter box is a fixed size and therefor has a certain media volume. A sponge the size of a gallon milk jug is larger than one the size of a child's glass. Rather than specifically measure media volume, we usually go with just knowing some generalizations. Media volume, from bottom to top, in major types of filters goes as follows usually: internal filters, then HOB (hang on back or "power") filters, then external cannisters, then finally "sump" filters. Undergravel filters (UGFs) are a special case, usable by the experienced, but I think they are way out of date technology for beginners, so I'll not describe them. Sumps are a bit more of an expert tool, requiring more setup knowledge usually, so I'll leave them out too. This leaves HOBs vs. external cannisters and usually its pretty safe to say that external cannister filters will have quite a bit more media volume than HOBs, allowing for much larger and more stable biofilter media.
OK, so what about ease of use? Well, its a pretty close call between HOBs and ECs (external cannisters) as either can be lifted away from the aquarium for a cleaning session with about the same amount of trouble or ease. ECs in the larger sizes have their hoses coming in to hose adapters that have quick release levers and adjustable flow controls. A couple of advantages of ECs is that they have the edge on silence, having no water noise unless you choose to agitate the surface a lot with your spraybar and they also allow a length of hose where an inline heater can be spliced to keep this function out of the tank. No heater in the tank makes for a nicer underwater scene. Most ECs also have multiple trays with handles for easy removal of each media type during cleaning.
TFF has happy users of all the major EC brands: Eheim, Rena, Tetratec and Fluval. One of the advantages of getting two of the same size and type is that you can just buy sets of supplies that are the same for backup or whatever. Having two filters on a big tank is nice because you can always clean them alternately and never experience a mini-spike in your ammonia and nitrite levels because of a cleaning. Ceramic rings, ceramic gravel, coarse sponges, fine sponges and floss are the typical media loads for these filters. They usually need cleaning once a month or much less and except for the floss, the media often lasts almost forever without replacement.
Well, I guess that's it for the latest installment of your filter book
... hope someone else reads it too after all the typing!
~~waterdrop~~
