DIY Flow diverter/diffuser
I've noticed that several people (like myself) are looking at ways of limiting the current (from HOB filters) in their tanks so as to not stress the fish and plants. Lots of different ideas have been tossed around from limiting water intake to using a rheostat to slow down the impeller in the pump... but I think you'll find this quite a bit easier and pretty much for free as most of you probably already have everything you need to do this little project.
20 OZ (591ml) Life Water/Gatorade style thick plastic bottle
Shears or heavy duty scissors
Box Cutter or Sharp Knife
Emery board or sand paper
That's all ya need!
First you need to remove the label from the bottle and wash the inside AND outside of the bottle.
MAKE SURE THAT YOU RINSE MANY TIMES TO REMOVE EVERY TRACE OF SOAP!!!!!
If you want to remove the label glue you're going to have to fill the bottle with very hot water, cap it, then scrub the glue off the outside with, again, very hot water and an abrasive kitchen scrubber.
If you don't want to bother with the glue you need to plan your cuts on the bottle so that the glued area is the part that goes over the rim of your tank so it's not in the water.
Now that it's clean it's time to section the bottle into three pieces. Check out the pic below. Find two ridges on your bottle, one near the top of the side of the bottle and one near the bottom. Using the valleys on the bottle will allow you to cut a straight line with your box cutter/knife and also the slight curving into the valley will give the diffuser the strength to keep from distorting from the flow.
In my case I didn't want to scrub off the glue so the cut you need to make from top to bottom is right along the right edge of the glue. This edge is folded back twice upon itself. Now there's no hard set rule on wide to make these folded over areas and is based on how thick the rim of the tank is that you'll be using it on. I tend to just make them about 1/2 an inch and just eyeball it.
Use your shears to round any sharp corners and such. Use the emery board/sand paper to smooth all edges that've been cut. This is a very important step as you don't want your more inquisitive fishes from injuring themselves on sharp edges. Sancho, my betta, actually goes into the diverter and 'plays' in the current.
Some people put put some gravel in the diverter to act as extra material for you bio filter to load up. You could put phosphate remover in it, or peat. I wrapped a chunk of Java Moss around a bit of lava rock. This works out great for me as the moss drags at the water flow slowing it greatly plus the moss gets first dibs on the nutrients in the water.
Now you may think "this can't work all that well" and it's good to question but here's a video that shows just how well this little thing works. This is my 1.5 gallon tank that's being filtered by a Marineland Penguin 100 Bio-Wheel filter. At it's best flow rate, the entire volume of water in the tank is being filtered about once every minute.
If you want to diffuse the water more you can drill small holes in the diverter. But a word of warning! If you do this you have to make sure that EVERY hole been deburred or your fish could easily get cut!
You can use .5L water bottles instead but the plastic is VERY thin and may not hold up over time.
I hope that this has been helpful to you all. I do not take credit for coming up with this general idea but I do believe that my version is superior to all that I've seen.
1G Planted Betta tank, 1.5G Planted Betta tank, 10G Planted Swordtail Fry tank,
10G Neolamprologus Multifasciatus (Shell Dweller) tank. Empty/Work in Progress 135G, 40GB, 2 x 20GL, 2 x 10G
My aquarium (and more) videos on YouTube