Fail-safe lower limit salinity for top-off planning?

[Who Dah?]

Hello,

I apologize if this has been covered, I Google'ed, but to no avail.

In your opinion (fellow reefers, please feel free to reply too!), what is an appropriate fail-safe salinity lower-limit to plan on for a top-off failure? I.e. if one's top-off unit fails and dumps top-off water (RO/DI water) into the tank, thus lowering the salinity, what would you want to limit that salinity drop to? The greater the lenience of an acceptable lower-limit, the less frequently one has to fill up their top-off reservoir, but the lower the potential drop in salinity as well. I believe there are two variables to consider (arguably 3):

1. The extra volume of water the tank's sump can accommodate in the event of a power failure.
2. The lower-limit salinity level one is prepared to accept in the event of a failure.
3. Although closely tied to #2, the sensitivity of the animals one is keeping. I.e. a typical FOWLR could handle a lower salinity than a typical SPS tank. (Obviously there are exceptions, but just speaking in general terms here.) But I think this third variable could just be incorporated into variable #2. Namely: what level am I prepared to drop to?

I'd be interested to hear answers in terms of two types of reef tanks and think that others reading this could interpolate the answers based upon their particular setup:

1. A typical SPS tank.
2. A typical LPS/ZnP tank.

Example:

1. Assuming my sump volume could handle the extra water with a power failure, I'd limit my tank to an ~15% 'sudden' drop in salinity due to a top-off failure on an SPS tank. Or perhaps in terms of actual measurements: a drop from 35 to 30 ppt, 1.026 to 1.022 salinity, 53.1 to 45.1 conductivity. Whatever units you like.
2. For a ZnP tank, I'd allow an ~20% 'sudden' drop in salinity due to a top-off failure.

Anecdotal references welcomed! I.e. "my SPS tank dropped from 1.026 to 1.021 overnight, I noticed it 2 days later, losses were great/minimal/etc".

Thanks!

 

[Up2no6ood]

If it were my mixed reef tank I would not let the salinity drop below 1.025. But then again I would never trust a salinity probe to control my salinity. I have 4 failsafes. 1: float switch to trigger ato, 2: backup floatswitch incase main float fails, 3: a 2 gallon container so even if my ato sticks it wont continuously fill, 4: I dose kalk with my ato so I have a ph probe that will stop the ato if the ph spikes. Is there ever a case that salinity will drop in a tank for any other reason besides a faulty ato or error in mixing during water changes? Maybe if you were skimming wet? If your salinity probe is accurate and dependable why not just set it for 1.025 and not worry about whether coral / fish can survive in a low salinity environment? I think for sps the drop in alk from low salinity would do most the damage.

 

[Who Dah?]

Heya,

I do appreciate the reply, thank you. But I intentionally attempted to leave out details on float valves vs. electronic ATO vs. probes vs. backups vs. swing-arms to help keep the discussion generic. I'm attempting to just plan for, and hopefully help others plan for, 'minimum lower salinity level tolerance due to a failure in which freshwater is dumped into the tank from one's top-off reservoir' and keeping the reasoning for the failure separate. Ya know? Pluses and minuses to them all, of course. But no matter what choice one makes in how freshwater is topped off, one can choose to what effect a failure will result in of course.

That said - you did answer what I was after: you wouldn't drop below 1.025 in a failure in which the #1 float switch fails due to a snail that got through your filter sock, and your #2 backup switches that your neighbors cat got into your house and chewed the wire on. Ha ha! I know, I know, not probable. But -- suppose they did fail. Your setup would only drop 2G of water max is what you're saying, resulting in a drop no lower than 1.025. Ya? I gotta hand it to you - that is a very tight worst-case scenario and I applaud you.

Thx!

 

[Up2no6ood]

If I calculated right adding 2 gallons of ro to a 25 gallon tank @ 1.026 would drop it to 1.024. I can say however that's there's this little run down lfs near me that runs their salinity at 1.024 their lps and softies seem to do fine but sps always looks horrible. This could be for a number of reasons but I attribute it to low salinity affecting cal and alk being they don't dose or run reactors. An if I had a salinity probe I would set it for as close as possible to your target salinity I mean why not

 

[Randy Holmes-Farley]

If I calculated right adding 2 gallons of ro to a 25 gallon tank @ 1.026 would drop it to 1.024.

Yes, that is correct.

 

[Randy Holmes-Farley]

I'm not sure I understand the use of the answer to the question. I think most ATO systems will keep salinity plenty tight unless it is a small aquarium.

If the top off fails, how is anything you do in advance (aside from limiting the reservoir size) going to limit the drop?

My concern with a poor ATO is the sudden drop in salinity from too much water at once, not a specific lower limit.

FWIW, I use limewater in my ATO, and overdosing that is more of a concern than ordinary fresh water.

 

[Who Dah?]

Quick Side note:
One quick back of the hand calculation is that adding 10% of your total system's body of water in freshwater to said body of water results in an approximate 10% reduction in salinity. (Technically 9% and change. But for quick math and 'assuming the horse is a sphere'. Ha ha! )

I.e. adding 10G fresh to a 100G body of saltwater, resulting in 110G of new total water volume, will reduce your salinity by (just shy of) 10%.

Heya Randy,

If the top off fails, how is anything you do in advance (aside from limiting the reservoir size) going to limit the drop?

That is exactly what I'm planning for. I hope to never have to be in that situation of course with preventative measures, but an ounce of prevention. I've read about too many people crashing due to a top off failure (or related kalk failure) that, IMHO, could have simply been prevented by limiting the size of the top-off reservoir (and/or limiting the amount of Kalk in their reactor). I am also assuming one does not keep their top-off water generator on at all times. I.e. not keeping their RO/DI unit on at all times filling up said top-off container (which I've seen too and, IMHO, is asking for a problem). So my original question asked another way, and a bit more specific, would be: what size top-off container would you use for 100G body of water to limit the possible sudden drop in salinity if it were to drop all of the top-off water into your tank 'at once'? (I'm randomly choosing 100G to help make the math easier and can interpolate accordingly.)

Theoretical and extreme Ideal answer #1 for tight salinity control in the event of a failure: 1G top-off container for 100G body of water. Now one has to fill up that container quite frequently, but that salinity isn't going to change much at all in the event of a failure.

Theoretical and extreme Ideal answer #2 so you don't have to fill up your top-off container but once a month: 50G top-off container for 100G body of water. Now one doesn't have to fill up their top-off container but once a month, but at the price of a practically guaranteed tank crash in the event of a top-off failure flooding your tank.

To date, I've been what I'd consider fairly conservative, IMHO, at accepting a possible ~10% salinity drop if my entire top-off reservoir were to dump into my tank following that quick math stated above. (But perhaps that isn't conservative enough, or at all?) I was just curious what you all do and what people's tanks have survived in this off chance.

Thx!

 

[Who Dah?]

Quick note - just saw that you use limewater and are concerned from that perspective: that line wasn't there on my initial reply before your edit. Excellent point! And hope it didn't sound like I was taking a stab at that technique in my reply as I did not intend to.

 

[Randy Holmes-Farley]

Instead of limiting the size of the reservoir (I don't, mine is 132 gallons), a better plan (IMO) is to limit the rate that the ATO might actually deliver top off water if it somehow got stuck on. If it is set to not much more than the normal rate of evaporation (by using a slow pump), then one cannot really get into a problem situation.

 

[Randy Holmes-Farley]

FWIW, getting a god quality float switch is also important. In 19 years, mine has never gotten stuck on. It is a big float switch in my sump.

This one, the Omega Engineering LV-1201 (bottom unit in picture):

Non-Magnetic Liquid Level Switches, Side Mount

 

[Who Dah?]

Non-Magnetic Liquid Level Switches, Side Mount

Wow - nice.

Instead of limiting the size of the reservoir (I don't, mine is 132 gallons), a better plan (IMO) is to limit the rate that the ATO might actually deliver top off water if it somehow got stuck on. If it is set to not much more than the normal rate of evaporation (by using a slow pump), then one cannot really get into a problem situation.

Not a bad plan! What about float valve users using gravity to top-off their tanks?

 

[Up2no6ood]

I would say that no matter how much evaporation your tank experiences the biggest container I would use for an ato would be 10% of total water volume and no matter how convenient it is never I repeat never top off directly from your rodi unit or automatically fill your ato contianer with rodi. Im not sure how muck kalk could dosed at one time before it leads to a catastrophic event but im sure that you would have to use a ridiculously small ato container to prevent such of an event. Im sure Randy could give us a fair estimate.

 

[Up2no6ood]

Instead of limiting the size of the reservoir (I don't, mine is 132 gallons), a better plan (IMO) is to limit the rate that the ATO might actually deliver top off water if it somehow got stuck on. If it is set to not much more than the normal rate of evaporation (by using a slow pump), then one cannot really get into a problem situation.

132 gallons of limewater! I wouldnt be able to sleep at night. Think I would have nightmares of my ato getting stuck in the on position

 

[rockslide123]

What I did to solve this problem is put my ATO on a timer to top-off 4 times a day such that the total time in 24 hours that the ATO is powered is less than the sump can hold OR the less than the desired salinity drop. For example: my Tunze is powered for 1.5 minutes 4 times a day and that will not even raise my sump level enough to trigger the back up float switch in my sump.
Keep in mind as you top off reservoir level decreases your pumping rate will vary.

 

[chill86]

I just run a tunze osmolator on a slow drip. It will only run for 8 minutes straight I believe so that equals out to about a cup of water the way at which I have the drip callibrated. I also run the sensors in my return compartment and there is a sponge in between the baffles that are before that, so no critters can get into the return compartment. I have been running it like this for the past 5 years and haven't had the first issue with salinty fluxuation. My return compartment was built as small as I could possibly build it, so it doesn't take hardly any water to reach the correct level. I am in no way affiliated with Tunze.

 

[authentic]

A question for the tunze people,my osmolator runs about a cup of water every time the power comes on,if it's on a timer are you figuring your evaporation has been more than that? And how do you turn the flow from the pump into a drip?

 

[Vermont05452]

Great stuff

Everyone has such good info. I never thought to have a ATO storage tank less then 10% of the tank volume. Makes total since. Thank you for sharing this.

I am shopping now for the best ATO set up for my tank upgrade. I would love to see some photos of people set ups for the ATO. Please share if you can.

 

[WolfInRed]

Hi all, my worst ATO issue was a failure in the apex Neptune that keep cycling the Tunze ATO and as most of us know when you power cycle the Tunze it turns the pump on, be nice if they fixed that 'feature'. I have a endless supply of make up water. The RODI makes water into a 5g bucket with a float. This removes the float from the tank as another level of isolation. The ATO takes it out of the bucket. So to protect the system I have the Apex input module with a few level sensors that will shut the ATO and pump to the display tank off if the water level raises too high. This does not prevent dilution from a tank leak that results in constant make up or siphen issues. The Tunze does limit the amount of water it will pump in before it errors and also has an upper level bacup float. Ultimately keeping a watchful eye on the tank and understanding the quarks of our system is the best solution to preventing catastrophic issues.