Figured it's time to start my first thread here.
I like to make stuff; see my signature for what I've been doing over the last... many years. Anyhow, our koi pond which has lasted 22 years is tired out and falling apart. The liner is getting stiff, the deck full of dry rot and termites, the overhead shading collapsed due to the same rot, and the concrete filter container (5' x 10') is developing a rather alarming tilt. Either gopher holes under it are collapsing, roots are raising it up, or both. Anyhow, time to start completely over again.
The pond is being redone and an all-new filtration system developed. I'm currently building a rotating drum filter with excellent guidance from Zoki51's thread, http://www.koiphen.com/forums/showth...137623-Diy-rdf. My build is similar enough to his that I can't claim any originality; you can read up about my few alternation over on that thread.
Anyway, as soon as that's done, next will be the bio section with a built-in UV setup, which brings us to this project. Picture will be added as things progress.
Years ago I made a 40W UV filter with Home Depot plumbing parts and while it didn't leak, it also didn't really clear the water either. This unit didn't use a quartz tube which is probably why it failed; I recently read that unless a UV bulb is run at around 100 degrees F, its efficiency drops way off. Exposing it directly to 63 degree water like I did meant that it was outputting about 1/3 the UV that it could have been (all while consuming the same power from the wall!).
It was later replaced by an 80W Emperor Aquatics unit which worked better, but like the previous unit it also failed to clear the water. I never did figure out why; it almost had to be too much water flow yet the measured flow and the UV unit did seem compatible.
I decided to go with a 120W bulb for not only for the higher exposure but also the longer dwell time due to the longer tube length. Because off-the-shelf 120W units are so expensive, the plan was to fabricate it. The bulb, sleeve, and ballast were about $300 from Pentair (who now owns Emperor Aquatic). I went with them because they're a huge aquaculture supplier and have all the Emperor spare parts, so hopefully they'll continue to carry them for many years.
The bio section of the filter will be built inside a black Intermediate Bulk Container (IBC), black because I read somewhere that the bacteria does better in the dark, so we'll see. Getting off track briefly, I tried many types of bio media: sponges, matts, lava rock, poly beads, but nothing did better (meaning: didn't eventually plug up) than simi-floating media* in a fluidized bed. A lot of people fixate on surface area and technically they're right, but after a couple years their claimed 50,000 sq. ft. surface area media is probably more like 500 sq. ft. due to internal plugging. The reality is that surface area is useless if it's not accessible.
Anyway, the IBC is about the right size that instead of building a standalone UV housing, the quartz tube could span the full width of the container. From there things kind of started designing themselves. First was the realization that the media can't be directly exposed to UV else it would always be, well, dead. So that meant shielding the lamp. Then there was how to get the water around the lamp while keeping the media away, as was how to access both the lamp and sleeve from outside the IBC. Currently there are several approaches bouncing around in my head:
- Have an assembly that resembles a capital "D", with the water leaving half way up the straight side. The UV lamp would be along the straight section and the sleeve extends straight out through the side of the IBC for maintenance. The middle curved part of the "D" would be the inlet side and is screened to keep media out, and the overall assembly shields media from direct UV exposure.
- Have a 4" tube extend straight through the wall of the IBC via a Uniseal to nearly the other wall, then have it branch off left and right to screened inlets of roughly 24" each in order to minimize media getting stuck to the screen due to suction.
- Slide the assembly to one corner of the IBC and instead have the pick up end run horizontally, allowing for a full-width inlet screen.
- Instead of branching off left and right, have a 90 degree bend turn upward to a vertical screened inlet. This is the simplest and cheapest but there may be an issue with media getting stuck to the smaller screen area compared to the other approaches.
Not sure which approach is best but a key plumbing component known as an "Elbow with heel" was purchased. The quartz sleeve will extend out through the "heel" while the water makes the turn in the large diameter section to flow into the pump. The elbow with heel is this one: https://www.grainger.com/product/MUE...rchQuery=3GUU7
*So far, the most promising (price vs. performance) semi-floating media seems to be: http://pentairaes.com/sweetwater-swx-bio-media.html. It's within a few percent of K1 Micro in surface area but costs about half as much and isn't as small.