Actually, having the aquarium chiller shouldn’t add any additional head pressure to your filtration system. The canister filter still has to move the water the same height regardless of whether it is pushing the water through the chiller or just discharging it directly into the aquarium.
Of course, the aquarium chiller does add more friction through the lines and this will reduce the output from the canister filter significantly, so I see what you’re getting at. There are formulas to help calculate how much effect each elbow has in that regard based on the diameter of the elbow and the number of elbows that are plumbed into the system, but there is a much more accurate way of measuring the flow rate in gallons per hour that the filtration is producing.
All you have to do is collect the outflow from the filter after it passes through the chiller, where it would enter the aquarium. Collect all of the water that is throwing through the system for 30 seconds, measure the volume of water that you collected, and then multiply that by 120. That will give you the actual flow rate for 60 minutes or one hour, with no guesswork involved. Then you can divide that number by the capacity of your aquarium to see how many times the tank is being turned over every hour.
You ordinarily want the filtration on a seahorse tank to be turning over the entire volume of the aquarium 3-5 times every hour. Personally, I would say that your seahorse tank is under circulated if it doesn’t turn over the entire volume of the aquarium at least five times an hour. So for your 49-gallon aquarium, you want the output from your filter/water pump to be at least 250 gallons per hour, in my estimation.
If the filtration produces turnover rates considerably in excess of five times the volume of the tank every hour, then you need to start to be concerned about generating too much water flow and too much current for the seahorses. If you have a spray bar return or waterfall return that diffuses the output from the filter, then you can achieve turnover rates of 10 times the total water volume of the aquarium every hour without producing too much turbulence and overpowering the seahorses. But if you don’t have a spray bar return or waterfall return that splashes the output from the filter into the aquarium and attenuates the water flow, then turning over the volume of your aquarium 10 times every hour may produce currents that can overwhelm the limited swimming ability of the seahorses, so be careful about increasing the turnover rate too much.
Good circulation is very important or a seahorse tank. But as with anything, too much of even a good thing can be undesirable, and too much current can complicate things for your ponies by making it difficult for them to swim, feed, and mate comfortably. One indication that you may have too much water movement in your seahorse tank is if the seahorses are getting buffeted around by the currents, and whisked away uncontrollably when they tire of fighting the current. Or alternatively, they may stay perched in one place all the time and refuse to swim around and explore their tank for fear of getting swept away by the current if they relax their grip on their hitching posts. So you can get a pretty good gauge of how well the seahorses are able to cope with the water movement than their tank by observing how the current affects the swimming ability.
Likewise, if a mated pair of seahorses is consistently spilling eggs during the copulatory rise, that’s another pretty good indication that there may be too much turbulence or water movement in the upper reaches of their aquarium.
If the seahorses are having difficulty tracking their prey and eating because the current whisks the frozen Mysis past them too quickly to target it accurately and slurp it up, that’s another red flag. Often that situation can be corrected simply by adjusting the output from your filter to reduce the current during feeding time or turning it off altogether while a seahorses are eating.
But as long as your seahorses aren’t getting buffeted around, aren’t routinely dropping eggs during disrupted mating attempts, and aren’t having difficulty targeting their prey and eating, there’s really no such thing as too much water movement. In general, the stronger the the water flow, the more important it is to keep the water currents steady and unvarying so the seahorses can establish holding areas in the sheltered spots and low-flow zones downcurrent without getting blindsided by unpredictable currents. Just make sure your seahorses are not getting trapped against overflows and be sure to screen off the intakes for any powerheads. Powerheads can be switched off at feeding time, if necessary.
Before you do anything else or consider adding another water pump, I would calculate the actual output from your filter as described above. Collect how much water it puts out in 30 seconds in a clean bucket, measure that amount, and multiply that figure by 120 see how many gallons per hour are flowing through your filtration system. Then divide that total by the capacity of your aquarium (~50) to determine how many times the aquarium is being turned over every hour.
Ideally, that calculation will come out to be around 5; if it’s lower than that, you can probably stand to increase the water flow a bit, and if the figure works out to be less than three, then you definitely need to step up the circulation. Likewise, if the number comes out to be considerably greater than 5, then you probably need to tone down the water movement somewhat, especially if you don’t have a spray bar return or waterfall return that diffuses the output from the filter. Remember, adequate surface agitation to promote efficient oxygenation and gas exchange at the air/water interface is just as important as the overall water movement.
If it turns out that you actually do need to increase the water flow and circulation, then you might want to consider upgrading to a larger canister filter with better output, or adding a powerhead with a shielded intake to the aquarium, rather than installing an extra water pump in line. That would make the plumbing much simpler and may be cost effective when you consider the cost of a new water pump.
Best of luck with your new seahorse setup, Sean!