I decided to do this because I was not happy with the other
DIY media reactors I was seeing on the internet. (especially the Gatorade bottle one

) I hope this helps someone out. Judging by the deltec reactor sizes, I think it should be ideal for at least 100+ gallons (probably 3-400 Max) and a minimum of a 200GPH pump.
To start you will need hole saws or a dremel to cut the holes in the top cap.
Start by finding the center in the cap and mark it. Take a 7/8" hole saw and drill out the center. Then use a 1" hole saw and drill out for the return. Then glue the 1/2" fitting female adapter in the center hole from the bottom of the plug with the and 1/2" Female adapter on the top of it. In the other hole glue in the 3/4x1/2" slip x thread bushing.
Next drill holes in the 3 x 1 1/2 bushing like the pic below.
The next thing I did was fill in a thin layer on the bottom of the knock out flange with 2 part epoxy so it was stronger and wouldn't break.
Glue the 3x1 1/2 bushing into the base. Make sure it is level. Next glue the 1 1/2x 1/2 slip x thread bushing into the 3 x 1 1/2 bushing again making sure it is in all the way and level.
The next step is cutting the 4" pipe. This part is tricky. I found the pipe ideally should be 19 3/4". The best way to check is to thread the cap into the female adapter and thread the 18" nipple in. You can dry fit everything and make sure the cap is screwing down onto the nipple when you thread it in. If you mess up and cut it wrong all you will have to do is make your own nipple with a piece of 1/2" pvc and two 1/2" male adapters. Also if you want your reactor taller or shorter that would be all you have to do to adjust it.
At this point all you have to do is make the diffusion plates. Take both 4" wafer test caps and cut off the lip on them. Then just sand down the sides some. Next drill a 7/8" hole in the center. After that drill a bunch of small holes for the water to pass through.
At this point you are mostly finished. All you will need to do is thread on the ball valve on the feed pipe and put on the 90s and insert fittings. You will also need to make the sponge filters to keep the media in the tube. This is easily done with some filter material and scissors.
On a side note it is best to use some wide teflon tape on the 4" plug so it screws in smooth.
I hope everyone enjoys this.
Here is a parts list and the prices to make this project.
$5.49 1 EACH 40CA40 SCH-40 CAP 4
$4.97 1 EACH PDFA40 PVC DWV FEMALE ADAPT 4
$.25 1 EACH 40FA05 SCH-40 FA 1/2
$.39 1 EACH 40FM05 SCH-40 FITT X M ADPT 1/2
$.48 1 EACH 40BUST0705 SCH-40 SXT BUSH 3/4 X 1/2
$2.13 1 EACH 80NI05180 SCH-80 NIPPLE 1/2 X 18
$1.07 1 EACH 40BUST1505 SCH-40 SXT BUSH 1 1/2X1/2
$3.74 1 EACH PDBU3015 PVC DWV BUSH 3 X 1 1/2
$4.90 1 EACH PDFFKO30 PVC DWV FLANGE W K/O 4X3
$.85 2 EACH ATC40 ABS TEST CAP 4
$1.39 2 FT CC40 FT PVC PIPE CELL 4" PE
$4.92 1 EACH 40BVT05 VALVE PVC BV WH 1/2 TXT
$.65 2 EACH 80NI0520 SCH-80 NIPPLE 1/2 X 2
$.29 2 EACH 409T05 SCH-40 SXT 90 1/2"
$.38 2 EACH INMA05 INSERT MALE ADAPT 1/2
Total $35.46 + Tax