Neptune AC3 PRO- DO probe $$$


New member
Hey Guys/Gals,

I have one that I definitely need the help of the RC gang on. I was just lucky enough to get my hands on a Neptune Systems AC3 Pro.

The unit came with the Temp Probe , PH and ORP probes.

Naturally the one I really really wanted was the one it didn't come with! I'm referring to the Dissolved Oxygen probe of course. Some might argue one of the most important parameters in a reef tank .

Naively I figured "oh no worries...I'll just jump on line and I'll have it hear by thanksgiving!" NOT!!! I hadn't looked up prices for these things before because I wasn't planning on getting my hands on a controller untill at least next year(thank G-D for craigslist!!!).These things are 450 bucks.

That's not crazy for this hobby, but I don't know. It just seems like a little " I got these folks by the short hairs " type thing going on.

Now... here is my question.

Every reefer is a tinkerer at heart I guess... so immediately the anti-establishment gene kicks in and I think " I can get around this dang it!"

So... these things (controllers) are basically "diluted" PLC's right?

Really all they do(in terms of the monitoring part not the controlling part) is sense either Resistance, Current flow or Voltage at the interfaces the probes connect to right?.

Then do some sort of look-up on some table and determine what that value references..

So for example a value of 3mA on interface 3(just pulling values out of me ear:0) would perhaps be 15 PPM of whatever (salinity or DO etc) or something just for argument sake..

SO in theory if i know the specs of the DO unit Neptune ships under their "flag" (if you like ) which is made by Oxyguard (THE name apparently in that field then i should be able to match a unit up to it that has the same tolerances, and ranges and get the same thing? Well and obviously figure out the pinout for the din or find a unit with the same interface.

Am I making sense?

A quick search on the internet yields lots of units for under a hundred bucks. I might even be able to match the very same unit right from OxyGuard and buy directly from one of their Distributors. It just wont say "Neptune" but who cares right?

I mean these guys provide DO measuring equipment to all sorts of water related industry including aquaculture. And some of their probes are under 100 Bucks!!!

Most of the folks they cater to are large business so it seems Neptune is REALLY playing the mark up game.

Personally, I think Neptune is sort of price gauging here cause they figure people will just pay it cause its "Neptune" blessed or whatever..

What do you folks think? Buck the system? Or just crack open the wallet?

Thanks guys for any insight and help !!!



New member
If you have good water movement and a skimmer, your DO will be fine. It's not needed imo and 99.99% of reefers don't have them and do fine. But if it's worth it to you then "crack open the wallet".


Premium Member
When I bought my AC3 I never inteded to go for the Dissolved Oxygen probe....bang for the buck - just didn't see it. I even question the utility of really having the orp probe. I got one but I don't react to its values; and I have read that you shouldn't chase the values you get from it. JMO.

The nerd in me says just crack your wallet....if you really want to update your bells-n-whistles go for it.


New member
For that price, you might as well go all out and get a Hach LDO probe, ~$1500, but they are so much nicer than normal, galvanic, membrane probes.



New member
Guys thanks for the advice. I'm thinking you are right. Actually it turns out i went down to pick up the unit and I had a surprise waiting for me. Freaking thing was an AC PRO not an AC3 PRO!!!! Big difference!!! Man was I hot. Well needless to say my mom's "if its to good to be true...." warning kept re-playing in my head on the way home.Oh well.. I guess you live you learn... its just if any of you have driven in North Jersey... you'll know what hell it can be on the Garden State South Bound on a rainy day before thanksgiving...a 1.5 hour trip took me nearly 6 hours!!!! And all for not.

On the Controller I'm still going to go for it and as far as the consensus I'm gonna just crack the wallet. Doesn't make any sense to spend almost 1K on everything else (base unit, software, PH probe,Temp Probe, ORP Probe, DC8, I/O breakout) and then cheap-out on the DO probe. Like buying a Jensen Radio for a Porsche! well okay maybe not quite like that but you get my meaning.

Well guys thanks a bunch again.


New member
Awesome. That's confirmation then it can be done! Sweet! No modification had to be done to the interface (6 pin DIN) or did pin-point specifically market it as a direct replacement for the Neptune model?