Auto Water change through skimmer

[Scott Allen]

Here is an idea I had that I am considering pretty seriously.

I am thinking of using my skimmer to automatically pull 2-3 gallons of skimmate out of my tank a day and have it drain directly outside. Then use my Apex with a conductivity module to tell a BRS 50ML a minute pump to add premixed saltwater to keep my salinity in check.

My current setup
- 210 Gallon display with apex controller.
- My auto top off is using a float switch and pulls directly off the ro/di filter

I'm thinking of leaving my current auto top off exactly as it is. Then adding the new conductivity module and BRS pump. I will set the conductivity module to pump the salt water for 30 min or less everytime it drops below 34ppt (1.025) The time will be whatever time it takes to bring it to 1.026 or so.

So.. my final questions are
- 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
- What's the most I would want salinity to swing over the course of a day?
- Is a constantly moving salinity of 1.025-.1026 a problem?
- How much salt would it take to move from 1.025 to 1.026 in a water volume of 180g+?

[Scott Allen]

The way I'm seeing this is that the skimmer is pulling out water now.. just a small amount in the form of skimmate. My auto top off keeps water levels steady based on a float switch. Now all that changes is when the float switch triggers, which will happen a little more often. Does it pull from a salt water bucket or from my RO/DI. The answer is determined by the Conductivity probe. Nothing else changes.

[Scott Allen]

After doing some math.. Correct me if a variable is off.. It would appear I should have little to no measurable salinity swing with this method

Assumptions:
180gallons of water volume (A higher number only works in my favor and this is an absolute minimum for my system)
New salt is mixed to saturation around 1.035
Skimmer pulls water out at a manageable rate for the BRS pump

So, I if I were to add .4 gallons of salt water mixed to 1.035 to 180 gallons of water sitting at 1.025... What would my salinity be? Here is the math.. I think

(180 * 0.025) + (.4* .035) = (180 + .4) * x While x = ending salinity level in tank

So then, x=.02502217294900221.. So that's the extent of the salinity swing per each addition!!

Meaning my salinity will be slowly moving between 1.0249999 and 1.02502217294900221over the course of each day.

[bluwtr]

One thing to remember Scott is that SG is temperature dependent. I would advise keeping your salinity as constant as possible, because that and rapid temp swings are strong stressors as I'm sure you know. I'm not sure I follow your math, but it seems right if you are only losing the small amount of water, but I didn't see where you account for evaporative loss. Of course evaporative will cause an increase in salinity whereas skimming is water level. Maybe you did and I just missed it, but of course what you are trying to accomplish would add depending where the water was lost and what kind--FW or SW. Personally I wouldn't let your SG get below 1.025. I think dropping down to .024 is more than you realize given the volume of your tank plus I think it would take a pretty long time for a skimmer to drop the SG that much.

Not trying to shoot holes in your idea (I think it rocks actually) just playing devil's advocate.

Good luck.

[Scott Allen]

The Ato would run seperatley triggered soley by water level as it is now. The salt would be dosed everytime the salinity drops below 1.0249999 (basically anywhere below the 1.025 mark) Then over the next half hour just shy of .4 gallons of water mixed to 1.035 will be added. Bringing my salinity up to 1.02502217294900221.... I'm talking extremely small numbers over the course of hours.

The big boogeyman in the closet seems to be the skimmer. What do I do if it goes nuts and pulls like 20gallons out of my system one day.. Is there anything that could cause that?

[Scott Allen]

I got my solution!!!! Set up a 5g bucket with a float switch. Have the skimmer dump into the bucket. When the bucket fills with skimmate, the float switch turns the skimmer off and sends me a message. From there I can tell a cheap maxijet1200 pump (or something similar) in the bottom of the bucket to empty the bucket to outside and turn the skimmer back on.. OR if there seems to be a problem (Like I emptied the bucket a few hours ago... why the hell is it full) I can wait to get home and see what's going on!!

Seeing as my primary filtration is live rock and my algae scrubber. This is no big deal even if I am gone for a couple days before I can get back!

Since I can control everything from my android phone and I get a chance to make the decision rather than a computer!! Skimmer problem solved!!!!!!

[bluwtr]

Okay, sounds good. Again as advocate, I would be wary of adding more float switches and more pumps etc. Just one more spot for the chain to break. As Gerwin loves to say K.I.S.S.

What ever you decide to do, make sure to take pics and post them. Very interested to see the system.

[Scott Allen]

Okay, sounds good. Again as advocate, I would be wary of adding more float switches and more pumps etc. Just one more spot for the chain to break. As Gerwin loves to say K.I.S.S.

What ever you decide to do, make sure to take pics and post them. Very interested to see the system.

Well played... And thanks to that thought.. I came up with a solution. I'm going to put a bulkhead in the bucket that drains back to the sump... So even no more than 5g can leave the system, and saves my floor from a potential disaster!

Also, I am going to dose the salt evenly throughout the day. I am going to set it up just like a dosing pump, and evenly add the amount of water I typically remove. Only use the probe as a guideline rather than the decision maker. That way the probe isn't making decisions for me. It will force me to pay closer attention to it and will remove the other failure point!

So now, I'm basically wet skimming into a 5g sized skimmer cup, and slowly replacing the water through out the day! Using a probe only to double check myself and with the bucket draining back to the sump... Disaster averted! Then I can remotely turn on a pump to dump the bucket at any time (the float switch will still email me and turn off the skimmer) and the whole system is stil automated!

[Gerwin]

or you could just turn off ato, pump out 3-5 gallons and pour in 3-5 gallons of correct salinity fresh salt or pump it in* probably take less than the time it takes to properly get your food ready to feed your fish, and have less stuff wired to the tank. Ultimately IMO the home aquarium should be something beautiful to look at, a accent to the home and less a science experiment in the living room, but thats me (and I am one big science experiment).
And 3-5 gallons done in 1 minute or 25 hours is not going to be seen as some great result in the overall health or the tank, another point to take into account is part of a standard ater change is detritus removal, rock siphoning etc. I wonder how much of this gets neglected when things become to "automated".

Food for thought

[Scott Allen]

Here is my plan.

Skimmer is plumbed to a 5gallon bucket with a bulkhead drilled at the 4 gallon mark or so that will dump any excess back into the sump. Giving me a hard 4gallon maximum before any else leaves and I have to make a decision (to remotely empty the bucket) The float switch at 2.5 gallons will warn me that the bucket is full and from there I can decide to activate the pump to dump the bucket to outside, or I can cut the skimmer off if I feel there is a problem (IE the bucket filled way faster than it should have)

The skimmer will be tuned to pull 2.5 or so gallons a day out and the salt pump will be programmed to dose 2.5 gallons a day back in (or the mathematical equivalent if I use water mixed to a higher salinity, which I plan too). The conductivity probe will only be used to monitor the salinity levels rather than as a decision maker. The ATO is unaffected by all this.

The biggest down side is I will need to tweak the salt pump each day to compensate for inconsistencies in the skimmer. But that's really not a big deal as we are talking small numbers on a big tank. This set up means that at most, I will have an additional 1.5 gallons of saltwater replaced with fresh water... Not a big deal at all on a system my size. (I can do the math if anyone is curious.. but I'll spare you seeing as I'm the only one that probably cares)

@Gerwin... The science experiment IS part of the hobby for me! And I don't think this will replace cleaning out the sump and detritus removal from time to time. But this will allow me to do that every 6 weeks rather than every other week (or get my FMFLFS to come do it ). (Does that sound right?)

[Gerwin]

sounds right

for what its worth to the reading public, I do not wanna sound like doubting Thomas all the time, but I do want to shed light on something that may not have been thought of and I always tend to look at things from a maintenance aspect as that is what I do every week.
That being said a great majority of my EXTENSIVE knowledge in this hobby is from looking at science experiments from YOU guys and gals. so I do not want to discourage you doing your own thing, we can all learn from it....
besides I love saying " I Told You So" and even more I love being told " Gerwin you were right" O can't decide which one I like to more