Auto Water change through skimmer questions

Awesome, thanks for the review of the conductivity. I figured it would take a bit to catch up. I'm hoping by using the conductivity to trigger a timer will solve it. At first I figured I would have the conductivity tell it when to turn on and off. But, especially after hearing this, I think it will be much better to just trigger a timer, wait a half hour then if the reading is still low, have the salt turn on again. If it's still low.. then I'm pulling Way to much out in the skimmer. And can have the apex set to email me a warning (and pump more salt mix in).

 

I think you have WAAAAAAAAAAYYYYYYYYY too much faith in technology. All electronics fail and malfunction at some point (especially conductivity meters BTW). If you trust your tank to a conductivity meter, you will crash your tank eventually.

That said, I know Randy Holmes-Farley does constant water changes. However, he uses a very accurate dual-head metering pump and uses the conductivity meter to monitor it and add redundancy. That really is the key; no automated system by itself is reliably. However, combining multiple levels of redundancy can greatly decrease the probability of a fatal failure.

I think Randy uses a duel head "Reef-Filler" pump by the way. They are not cheap though and still require constant monitoring and tweaking...

 

I don't have that much faith. I also don't mind constantly monitoring my equipment. I recalibrate my probes at the beginning of every month anyhow. Just to guarantee accuracy. It takes a couple minutes and calibration fluid is cheap.. so why not. As long as I don't get too comfortable with it being right, I shouldn't have any problems that a normal ATO couldn't cause.

The only thing that is really happening is dosing salt based on a conductivity probe. I currently base all my judgement about salinity levels off a tool that is just as likely to be messed up (a refractometer has to be adjusted as well)

 

Possible Failure points:
1.) Skimmer pulls too much water out - Always keep salinity bucket 1/3 or more full to compensate

2.) BRS pump gets stuck on - Email warning from apex on both salinity levels and pump settings

3.) BRS pump gets stuck off - Email warning from apex on both salinity levels and pump settings

4.) Plumbing Clogs not allowing skimmate to leave cup - Clean and flush plumbing every time I clean the skimmer cup (weekly or more)

5.) Conductivity probe needs recalibration - Recalibrate every month and double check salinity of tank against refractometer weekly/daily


Anything else I'm missing? (I know there is lol)

 

A few thoughts

A) Lots of things can mess up the conductivity meter besides calibration. Equipment fails, causes stay voltage, messes up conductivity meter. RF interference. Algae growth. Bacterial films. Ect... Also, as pink4miss said, the probe will have delays, they are not real time.

Not sure what you can do. I guess e-mail if out of a certain range. However, the purpose of this is to avoid parameter swings and the most important parameter to avoid swinging is salinity. Just food for though.

B) Skimmer overflows due to some contaminant
You can limit the amount of water you put in, but what about take out? I guess you could set up a collection bucket for the skimmate, set slightly below the skimmer cup, but above the top over the top of the aquarium. Add an bulkhead overflow to the top of the collection bucket, then if too much is taken out, the rest will go back into the tank.

C) Murphy's law and Everything else I haven't though of LOL.

Also, to answer your questions:

"- Is there any reason I shouldn't mix the salinity beyond 1.026 (allowing me to do say 40-50g of water change out of only a 30g container?) Using my auto top off and tank water to dilute the mix"

You can do this. The water will saturate at around 45-50ppt or about 1.034-1.038, so, this will limit how much you can add.

"What's the most I would want salinity to swing over the course of a day? "

Any swing can be stressful. There can be swings do to evaporation without an ATO, but that is usually still only a percent or so per day. 10% (or sometimes less) above or below natural salinity, for an extended period of time can be fatal. I haven't seen much data on short-term swings, but based on my experience, I wouldn't want to see much more than about 5% swing per day, less is better though.

- Is a constantly moving salinity of 1.025-.1026 a problem?
Should be okay.

- How much salt would it take to move from 1.025 to 1.026 in a water volume of 180g+?

Edit sorry I realized I answered the question wrong. I'll fix latter when I have a minute to do so.

 

Just a couple of silly questions regarding the "failure" e-mails:

1) How far out of town might you be when you receive one?

2) Is there someone else there who is trained at troubleshooting your system whom you can trust NOT to be at the mall at that moment?

 

Is it any different than the risk inherent in using any form of auto top off?

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Hmmm... Guess not.

 

When talking about a 210 gallon tank, I have a lot of room before you can even measure a change. The salinity shift is going to be extremely low. We are talking 1%s here. With a smaller tank the tank would experience swings. But we are only talking a max of 2-3% water loss/exchange over the course of an entire 24 hour period. And by applying with a dosing pump, you never have a point of quick shift.

 

I disagree, there are more variables and therefore more things to go wrong. Granted they will go wrong slowly, but to monitor it all the time is going to be a lot of work.


Anyways though, to answer the salinity question, you had asked about adding salt. I had given you evaporation, but addition is more tricky as it depends on the salinity of the saltwater added.

So, for this let's just say your top off salt has an s.g. of 1.035.

Then there are two questions, do you want to change or add water?

To change water:

You start with 180g @ 1.025 and want 180g @ 1.026

So, you have:
(180*.025) + (X * .035) = 180 * .026
So, if you do the math, x = 5.14g

However, if you really want to add, not change, then your starting with 180g @ 1.025 and want 180 + x @ 1.026

So, you have (180 * 0.025) + (x * .035) = (180 + x) * .026

So, if you do the algebra, x = 20g, but you now have 200g in your system. See how you could start running into problems?


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