DOS issue with air bubbles slowly forming

tiggs · Jul 6, 2018

Strange issue with my DOS. Both lines are completely primed and calibrated and work fine until I set them up on my tank. I run a sump-less AIO, so the lines go directly to the rear compartment of my tank and are held in place by a zip tie facing downward. Once they dose for the first time, a small air bubble starts forming at the tip (where the liquid comes out) and slowly starts getting bigger and working its way back through the line. Eventually, it loses prime.

The DOS is supposed to support up to 24' of head pressure, so I wouldn't think 2 feet up and 3 feet over would cause an issue, but here we are. Anybody have any ideas or experience with a similar issue? I've opened a ticket with Neptune, but figured it was worth asking here too. Thanks

Waters · Jul 7, 2018

I have had this issue since I started using them over a year ago....doesn't seem to affect the dosing amount though. Are you using Neptune air tubing? If you use regular air tubing it will start forming air bubbles pretty quickly......the Neptune stuff must have a thicker inside diameter.

tiggs · Jul 7, 2018

Yeah, it's strange. I've been using Neptune tubing, but my unit was also lightly used, so I've ordered replacement tubing, a line holder, and actual reservoirs with the feed line. I'm hoping this sorts it out.

Clownfishy · Jul 8, 2018

I have the issue on one pump and not the other but I can also confirm it does not seem to affect the actual dosage!

roberthu526 · Jul 21, 2018

If you lose prime then it’s going to impact your dosing amount I think. Sounds to me the dosing head is not tightly secured so air can pass through the tubing that is pressed by the head. Maybe reassemble the head?

tiggs · Jul 21, 2018

I ended up working with Neptune and a new head fixed the issue. The issue was primarily only affecting one of the pumps, so they gave me a free one and I purchased one. Since then, no issues at all.

Clownfishy · Jul 22, 2018

I have replaced the connector going into water container and I no longer have bubbles being drawn into the dubbing so maybe worth checking the connector.

Jim Bertone · Sep 16, 2018

Have had similar issues with the Water Remove line. It is setup through the wizard to do an auto water change. Actually saw it in action once, the water fill pump was spinning in the right direction and the water remove was spinning in the opposite direction. That's right... it was pulling air from the open line sitting in the sink.... So I reprimed the unit, added a small bucket in the sink to catch the removal water and checked operations. Was working great and went to bed. This morning the sump is nearly full and the catch bucket has 80 mls in it. Time to call Neptune.

redpine42 · Sep 16, 2018

tiggs said:
Yeah, it's strange. I've been using Neptune tubing, but my unit was also lightly used, so I've ordered replacement tubing, a line holder, and actual reservoirs with the feed line. I'm hoping this sorts it out.

I'm using DOS/DDR and having similar problems. I've been working with Neptune and there solution is to redo all your hosing. The problem, in my opinion, is the hose connections to the head. The screw on nuts loosen and the whole connection is not that good. It's a poor design that doesn't keep pressure. I get it fixed for one day and it comes back. I would not recommend DOS and DDR. Don't waste your money on DDR, I've had problems with it too leaking.

redpine42 · Sep 16, 2018

tiggs said:
I ended up working with Neptune and a new head fixed the issue. The issue was primarily only affecting one of the pumps, so they gave me a free one and I purchased one. Since then, no issues at all.

I've had this problem in 3 out of 4 heads. Really hard to stabilize tank parameters when your dosing is inconsistent.

Thinking about buying new heads and trying.

Teddyboy16 · Oct 1, 2018

The head units do wear out and need to be periodically replaced. I can’t recall what the recommended replacement time interval is.
The connection points on the dos head units can be problematic. If your head unit is taking in air specifically on the intake, you can use this: https://www.freshwatersystems.com/p-3036-john-guest-female-adapter-nptf-polypro-14-x-14-nptf.aspx

People typically use them on both ports. They screw directly onto the connection point once you remove the nipple, but you have to cut the tip off of the port in order to get the fitting to seat properly. Otherwise you won’t have a good connection. Apply a little Teflon thread paste or even silicone sealant to the threads before you screw the fitting onto the port. They are a polypropylene body with EDPM o-rings so they are reef safe. Since they are a John guest fitting it’s important to make sure the cut end of the tubbing is square. You can do this by using a single edge blade or exacto knife. Cut it on a flat surface with the blade perpendicular to the table surface. You can also use a R/O tube cutter, and you’ll get a square cut every time. It’s a couple of bucks from BRS.

The square cut tubing requirement applies to the DDR as well since it has John guest fittings too. A common problem is not making sure the tubing is fully seated into the fitting, or the cut end of the tubing is not square. One or both issues combined can cause air intake. Sometimes people insert the tubing and immediately feel resistance and stop. You have to push through that first initial resistance which is the oring so it fully seats square at the bottom of the insertion point which should eliminate air leaks.