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Need help calculating salt usage...


realypk

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So my 75 is finally at that stage where I've got everything relatively nice and stable, corralling growing etc but I have an issue i dont know how to get arround... How do i know how much salt my tank is using? Salt creep and skimming all seem to be adding up to quite a bit of salt use!!! I dont do many water changes because my PHO and Nitrates are all very low, my biom seems to be eating everything up readily. Yesterday some of my corals looked "off" LPS retracted etc. So I checked and to my shock i was at 1.23 SG much lower than the norm 1.26 i normally run at. I'm slowly getting it back up, today its at 1.25. My question is how do i get to know how much salt I use, to where i can just put in X of salt per day to avoid changes.... Do I take daily salinity measurements? Then is there some sort of calc based off my water volume + loss rate that equates to a measurement of salt?

 

Thanks!

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You may have a misconception about water changes and why they're done. Ideally, you don't do water changes to manage nitrates and phosphates. That's what your biological filtration (rocks, sand, clean up crew) are there to  manage. We perform water changes to replenish inorganic trace elements that may not be otherwise replaced; to remove otherwise unskimmable (nonpolar organics) pollutants from the water; and to restore/manage ionic balance over the mid- to long-term. 

 

As for your salinity question, when you find a salinity imbalance, depending upon the size of your system, you can add saltwater to your sump when salinity is low above the ATO level, or substitute saltwater instead of fresh in your top off for whatever time is needed. Evaporation will continue to occur, gradually concentrating the total salt in the system and raising salinity until you reach your target level again. This approach is better than adding dry salt to your tank because, as it is, the dry salt mix is slightly caustic and, ideally, should be mixed a day or so in advance to allow the pH to stabilize and the newly mixed water to achieve balance with the surrounding air.

 

 

 

 

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(edited)

About 2 weeks... I do have a fair bit of salt creep that I whipe away every other day ( i push in the nuggets that are convinient) But i didnt think it would be that big of a deal. I checked my calibration with fluid and salt tester unit is still well calibrated...

 

So a little under 2 weeks to go from 1.026 to 1.023 I have around 100 Gallons in the total system when you include the sump I'd have to get some measurements though and dont know how to calc for rock/sand displacement. 

 

@Origami As far as trace elements I am currently doing the ATI 3 part dosing system to replace trace element issues. I guess only issue I would have is unskimmable organics, can you explain those to me and seeing as I'm doing the ATI 3 part what would a "reduced" water change recommendation be for those to keep them safeish. Water changes are just very inconvenient (Wife aggro as well as time consuming) in my current situation so I'm trying to do as few of those as possible an so far have gotten away with not that many. 

Edited by realypk
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That's a lot of salinity drop. You must be skimming very wet to lose that much salt, or you have a bubble problem resulting in a lot of salt creep. Here's what I find strange:

 

You have 100 gallons of saltwater. That's about 379 liters total with a total weight of around 387 kg. Now, you've given us a starting and ending salinity of 34.51 ppt (1.026 sg) and 30.55 ppt (1.023 sg). From these, I can calculate approximately how much salt you have in your water. At the starting salinity of 1.026, you have about 13.36 kg of salt in the tank. At 1.023 sg, it's closer to 11.58 kg. That's a drop of about 1.75 kg, or just under 4 pounds of salt. That's one heck of a lot of salt to lose in 2 weeks. To visualize that more clearly, it's the amount of salt that you'd find in a bit over 13 gallons of your water at it's starting salinity. In other words, neglecting salt creep as a method of export, you'd have to be losing upwards of 13 gallons of water through your skimmer or through some other leak over a two-week period. Another way to visualize it is to note that a cup of IO weighs around 0.6 pounds. Therefore, you're losing about 6.5 cups of salt over two weeks, or about a half cup a day.  So,

 

  • You've either got a big leak somewhere (unlikely, because a gallon a day of loss would probably be noticed).
  • You've got a huge amount of salt creep that you're picking off and discarding - about a half-cup a day of dry salt.
  • You're skimming really wet, exporting close to a gallon a day of skimmate.
  • Or, of course, a combination of the above.

Another option is that you're not calibrating your salinity measuring tool correctly.

 

Your dosing approach will replace many trace elements. That's the good news. Over the long haul, though, any one of the two- and three-part systems will ultimately result in an ionic imbalance. For example, in basic two-dosing, you replace calcium and alkalinity using mostly calcium chloride and sodium bicarbonate (or sodium carbonate). You'll notice that, while dosing to replenish calcium and carbonate alkalinity, you're also adding sodium and chloride ions. Now sodium and chloride are in huge supply in your water, so the added amount is small relative to what's already there. But, over the long term, these small additions add up and can shift ionic balance. That's why, even in these sorts of systems, you want to perform an occasional, major water change. 

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Oh, you asked about unskimmable organics. It pays to understand basically how a skimmer works first.

 

A skimmer introduces millions of tiny bubbles to a body of saltwater. Each bubble has a boundary - what we'll call an air-water interface. It's the boundary between the air that's trapped in the bubble and the water that the bubble is floating in. Water itself is a polar molecule and that's a very important property when it comes to dissolving things. Now, we have lots of different kinds of organic molecules in the water. Some dissolve well in water - we call these water-loving or hydrophilic behavior. Others don't dissolve but instead repel water - we call those water fearing/avoiding or hydrophobic behavior. Some organic molecules, because of their structure, are hydrophobic, some are hydrophilic, and some are a combination of hydrophobic-and-hydrophilic. It's this last class of organic molecules that tend to be attracted to the air-water interface of the bubbles in the skimmer with their hydrophobic ends hiding inside the bubble and their hydrophilic tail pushed out into the water. The other stuff - especially the hydrophilic molecules have no special attraction to the bubbles, so they tend to stay behind in the tank water. These other organics often can be addressed using activated carbon or water changes.

 

BTW, as these organics accumulate, your tank water begins to take on a yellow-cast. It's difficult to notice most of the time. However, if you tape a piece of white paper to one end of the aquarium and look at it from the other end of the tank, it'll look a bit yellowed (under white light) if the water is full of dissolved organics. The Germans call these yellowing organic compounds "gelbstoff" or yellow stuff.

 

 

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I was about to chime in but @Origami hit the nail on the head with his scientific and quantifiable explanation of both general topics.  I’m actually impressed as his explanation of how the skimmer works is the basics of cell biology.

 

Just to to elaborate on one point though, with 3 part dosing it is expected to see an increase in SG.  So by you seeing a decrease points to a possible larger problem.  Is it normal to see such a large decrease in specific gravity, and how much/how often do you top off fresh water? If you changed your return pump, or had to adjust your full siphon valve lately, this could account for a one-time change in salinity.

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(edited)

First off your analysis and explanations are amazing! Thank you for taking the time!

 

The skimmer currently exports about half gallon per 2 days. Is this too much? The skim looks kinda gross and smells slightly.

 

Secondly i did add a few frags which i used tank water to dip and acclimate so that accounts  for maybe 2 gallons in that period. I used approximately 10 gallons of rodi over that period but i wasn't tracking it diligently.

 

I can tell of no wetness around the tank and creep seems normal.

 

 

Here is my planned action course of action :

- Take your advice on whatever skim rate i should aim for.

- Fill my Rodi storage completley so I have a good guage. 

- Take accurate measurements of sump water content.

- Get my tank to 1.026 salnity. (Is there a more accurate measurment unit? The hannah can do ppt(.1), psu(.1), sg(.001)

-Take salinity readings daily and record them. I won't add anything over the next week (other than normal feeding and dosing)

 

Would 7 days of data be sufficient?

 

----------

Also what would you consider major water change and how often? Should i just do the paper test and if slightly tinted do a change?

 

 

Edited by realypk
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On a 75g even assuming heavy stocking and heavy feeding, it would appear that you are skimming too wet.  I normally shot for a nice dark, almost “black tea” color.

 

As for water changes, it really depends on why you will perform them as there are now additives and better equipment that handles much of the tasks they’ve been used for in the past.  (Ie. export nutrient, replenish elements, normalize ion levels, remove contaminants, etc.)

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Any removed saltwater should be replaced with saltwater. We only add freshwater (RODI) to replace evaporated water since salt doesn’t evaporate. Every tank is different, but many recommend 10% water changes each week. Others prefer bigger and less frequent water changes. Find what works for your tank and you and roll with it.

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(edited)

Understood I'm going to take the data sets daily to see exactly how much salt im loosing, only using rodi with ATO for replacing evap so that should not be an issue. Is there a fancy calculator that lets you make the salt calculations you got @Origami?

Edited by realypk
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My question is why not keep things simple? Skim a little less wet by adjusting the skimmer. Also, where are you getting all that salt creep?   Some is normal, but it shouldn’t be excessive to the point that it makes a difference. I would fix the issues and the salinity fluctuations will minimize. Salinity stability is very important to the tank’s inhabitants. 

 

If you choose to skim so wet then sounds like you already calculated the volume. Replace the removed water with new salt water (same salinity as your tank) in the same volume. You do not want to add dry salt to the tank so not sure why you want to calculate salt loss. You should mix it beforehand. It is ideal to let it mix for a while e.g. 24 hrs to let the carbon dioxide stabilize which normalizes ph. 

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BTW replacing wet skimmate often with new saltwater is a form of water change. It’s just more maintenance than many of us are willing to deal with :). What happens if you go on vacation? Ideally you have the tank stable enough that only fish need to be fed and the tank is ok without daily maintenance.

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(edited)

I wasnt aware that you could just replace skim 1:1 as i figured skim would be ultra concentrated so higher in salinity value.

 

I currently have a nice reservoir that the skimmer feeds with an auto aqua skimmer cutoff if it gets full so i usually dump the skim every 5 days or so, vaca id dump then go and let the thing just fill and cutoff 

 

Ive dialed the skim down so well see how this goes. Salt creep is mostly in the sump area and in the lids nothing super excessive compared to what ive seen on other tanks

Edited by realypk
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16 minutes ago, realypk said:

I wasnt aware that you could just replace skim 1:1 as i figured skim would be ultra concentrated so higher in salinity value.

 

I currently have a nice reservoir that the skimmer feeds with an auto aqua skimmer cutoff if it gets full so i usually dump the skim every 5 days or so, vaca id dump then go and let the thing just fill and cutoff 

 

Ive dialed the skim down so well see how this goes. Salt creep is mostly in the sump area and in the lids nothing super excessive compared to what ive seen on other tanks

It’s a good start and should minimize fluctuations. You should monitor salinity to verify. Good to monitor more often until you find it stable. I used to monitor weekly, but go much longer now.

 

This is an interesting article http://reefkeeping.com/issues/2006-08/rhf/index.php

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Understood I'm going to take the data sets daily to see exactly how much salt im loosing, only using rodi with ATO for replacing evap so that should not be an issue. Is there a fancy calculator that lets you make the salt calculations you got [mention=2631296]Origami[/mention]?
Unfortunately, no. Not for most of what I wrote. However, I'll often look up and use a salinity converter (such as the one here: https://www.hamzasreef.com/Contents/Calculators/SalinityConversion.php)

But that just enables me easily go from sg to ppt for artificial saltwater. The rest of the calculations just follow by application of other knowledge.
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You mentioned a 75g display but estimated 100g in the system; how large is the sump? I have a 75g display with a 30g sump but have 74g of actual water volume.

 

Half a gallon of skimate every other day is a ton! Pretty sure this is seven or eight days worth for me (this isn't to say you should or shouldn't have the same amount, just an example).

 

32938345048_eb0ff77100_b.jpg

 

 

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Yea mine was much much clearer and see through so I'm presuming this was a source of the problem. I've dialed it down significantly but it doesnt seem to produce much, when i try dialing it up just a tiny bit more then where it is now it goes nuts and skimms quite a bit. I'll leave it running at current settings for a few more days and take a pic of the skim for reference. 

 

Also good news is tank is holding at 1.026 steady for 2 days now and ato has not used nearly as much water...

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Might give some details on the skimmer. What brand and model? If it's not recirculating, then you might try to raise it up a little and adjust the valve then. Some skimmers tune better than others. The trick is to find a good sweet spot and then let it be.

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On 1/18/2019 at 3:11 PM, Origami said:

To visualize that more clearly, it's the amount of salt that you'd find in a bit over 13 gallons of your water at it's starting salinity. In other words, neglecting salt creep as a method of export, you'd have to be losing upwards of 13 gallons of water through your skimmer or through some other leak over a two-week period. 

 

On 1/18/2019 at 7:52 PM, realypk said:

The skimmer currently exports about half gallon per 2 days.

 

1 hour ago, realypk said:

Yea mine was much much clearer and see through so I'm presuming this was a source of the problem.

 

I'm not so sure you've fixed the entirety of your problem. As Tom said, you're "missing" enough salt for 13 gallons of water. You skim 1/2 gallon every 2 days. In 2 weeks, therefore, you've skimmed 3.5 gallons. That's only 1/4 of the missing salt. 

 

If the last statement I have you quoted in here represents how/where you think the majority of the missing salt went, then I think there's still another explanation. I've had my tank before where after a water change I would have sworn I had one reading, only to take it a second time and get another. Bubbles on the refractometer will make results goofy - even little ones I've seen skew it. I always take at least 2 different readings before I start trusting it.

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Very interesting... could very well be I usually just took a reading soon after mixing and if it read right considered it good to go and dumped it in the tank. Didn't really think much about bubbles. So perhaps the water I was replacing was wrong or even worse it was wrong to begin with. Part of the reason I even noticed this was because I recently upgraded to a Hannah Salt Tester which instantly made me go "huh..." beause my old refractometer told me i was at 1.026 and my hannah told me i was at 1.025. Its always been hard for me to read the things due to my goofy eyes and I knew I was close but the digital output of the hannah leaves no question, so perhaps it is indeed a mix of both over skimming and also reading my old refractometer slightly wrong. 

 

Question, as far as skim goes, is skim the same salinity as tank water or does it export extra salt in comparison to normal tank water. IE should I replace it with 1:1 with mixed water or should I use some other salinity level for lost skim?

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I’m guessing one of the 2 salinity readings were off and that’s the main reason for any confusion.

I’ve worked on tanks that use the ATI method and all of them eventually needed water changes.

In my opinion, it’s just easier and cheaper to go with 3 part dosing and a regular bi-weekly water change of 25g.

This should take 1 hour every 2 weeks- cake.

What are your nitrates and other parameters at?

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Yea I'm guessing I've been having salinity swings and didnt really notice till I got the hanna tester which made checking it so easy that there was no reason for me to not frequently do it. 

 

Below are my stats, rather stable at that, the par reading is def off as the sensor is askew and not really facing the light well. 

image.thumb.png.6e7cb4b4dd46fd3b740a67654e5e0338.png

 

I can take PHO, Mag, Alk etc later when I get home, but so far everything looks pretty healthy. 

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Before changing anything else, just monitor you parameters (SG and daily RODI addition) for changes/trends.  The next thing I’d work on is dialing in the skimmer to a skimmmate that resembles that of @madweazlphoto.  I think most shoot for a similar color as it is a fine balance of high export and lower maintenance.  When dialing in the skimmer also take note of the water/air interphase (a noticeable line where it seems like the water level stops and everything above it is just bubbles).  Usually the sweet spot for this line is right at the neck of the skimmer.

Since you pointed out that there aren’t any leaks and salt creep isn’t extreme, the skimmer is likely the culprit.  

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