Coarse, continuous salinity adjuster

[NetMax Aquaria]

I'm designing a brackish biotope of around 700g. The plan is to use a continuous trickle water changer, around 15-20ml/minute to cause a 10% per week water change. This will give me very stable parameters in regards to toxins, and the salinity will vary slightly (which is desirable for brackish fishes). Is there a simple low-tech method to add salt on a daily basis. At its crudest, I could make a fine stainless steel mesh box, partially submerge it in the sump, and install an auto-feeder above to roll out some grains of salt. I don't know the calculation, but the setup could be adjusted on the fly as needed. Wondering what other options might be available for this application, as metering grains of salt may present long term issues, and I don't have a sense of how often I'd need to refill an auto-feeder cartridge (to daily built about 10g of freshwater to eventually full marine salinity when the fish are adults). Thanks for reading and if you have any suggestions.

 

[Reefing102]

So 10 gallons a day, at rough brackish levels is about 2.5 cups of instant ocean (I think).

So with that said, 20ml per minute is about 1200 ml per hour or about .317 gallons per hour. One half cup of instant ocean makes a gallon of full strength sea water. So a quarter cup per gallon should be roughly brackish levels.

So using very rough numbers, you would want to add about 1/8th cup of salt per hour. Perhaps there’s a large autofeeder that could do that. But I don’t know.

Me personally, I’d just have a premixed brackish water mixing tank and connect the auto water change system that way. If the salt level, within reason, doesn’t truly matter to brackish (or you want it to vary), you could always mix it up a bit by adding more or less salt to the mixing tank thereby varying the salt levels through out the week or so.

 

[griss]

Me personally, I’d just have a premixed brackish water mixing tank and connect the auto water change system that way. If the salt level, within reason, doesn’t truly matter to brackish (or you want it to vary), you could always mix it up a bit by adding more or less salt to the mixing tank thereby varying the salt levels through out the week or so.

This is how I would approach it as well.

 

[NetMax Aquaria]

So 10 gallons a day, at rough brackish levels is about 2.5 cups of instant ocean (I think).

So with that said, 20ml per minute is about 1200 ml per hour or about .317 gallons per hour. One half cup of instant ocean makes a gallon of full strength sea water. So a quarter cup per gallon should be roughly brackish levels.

So using very rough numbers, you would want to add about 1/8th cup of salt per hour. Perhaps there’s a large autofeeder that could do that. But I don’t know.

Me personally, I’d just have a premixed brackish water mixing tank and connect the auto water change system that way. If the salt level, within reason, doesn’t truly matter to brackish (or you want it to vary), you could always mix it up a bit by adding more or less salt to the mixing tank thereby varying the salt levels through out the week or so.

Thank you Shane for quantifying the rates. The 2.5-3 cups/day is possible in a larger Koi pond auto-feeder, but I don't have the head space above the sump. I'd forgotten how much physical salt was needed. The tank will be built into a wall unit, end to end, with little space above, behind or adjacent for a brine tank. Do you roughly know how dense the brine could be, to size a pressure container in the basement underneath? For example, if I brought a brine to saturation, what ratio of brine to fresh would be needed to hold brackish conditions. The design would then be bringing two 1/4" lines up, (brine + fresh), valving them to a ratio, and then I adjust them both up/down to change water change %..

 

[Reefing102]

I’m not an expert in the field, but my understanding is saturated brine is about 26% salt. Saltwater/reef tanks are about 3.5 percent.

In this particular case to calculate how much salt you want to reach saturation, is likely easier to to do a weight measurement. A gallon of water is roughly 3776 grams. At 26 percent, that’s 981.76 grams of salt per gallon or roughly 2.16lbs of salt per gallon to reach saturation.

A 5 gallon bucket of instant ocean salt is 48 lbs, so round down, you can get about 24 gallons of saturated brine per bucket.

Given the specific gravity (sg) of saturated brine is roughly 1.1975, we just need to calculate how to dilute it to roughly 1.015 (or whatever your target brackish concentration desired).

This is where things get complicated (primarily as I can’t find a calculator for it), but you would need to drop the sg by roughly .1825. Not sure if he’s on here anymore but @TheH may be able to adjust his calculator to be able to calculate it (it currently doesn’t go high enough). Or perhaps, @Randy Holmes-Farley may be able to chime in with the calculation. But I think the brine to freshwater ratio may be pretty significant. I apologize as I don’t have a solid answer for you.

 

[NetMax Aquaria]

I’m not an expert in the field, but my understanding is saturated brine is about 26% salt. Saltwater/reef tanks are about 3.5 percent.

In this particular case to calculate how much salt you want to reach saturation, is likely easier to to do a weight measurement. A gallon of water is roughly 3776 grams. At 26 percent, that’s 981.76 grams of salt per gallon or roughly 2.16lbs of salt per gallon to reach saturation.

A 5 gallon bucket of instant ocean salt is 48 lbs, so round down, you can get about 24 gallons of saturated brine per bucket.

Given the specific gravity (sg) of saturated brine is roughly 1.1975, we just need to calculate how to dilute it to roughly 1.015 (or whatever your target brackish concentration desired).

This is where things get complicated (primarily as I can’t find a calculator for it), but you would need to drop the sg by roughly .1825. Not sure if he’s on here anymore but @TheH may be able to adjust his calculator to be able to calculate it (it currently doesn’t go high enough). Or perhaps, @Randy Holmes-Farley may be able to chime in with the calculation. But I think the brine to freshwater ratio may be pretty significant. I apologize as I don’t have a solid answer for you.

Your calculations have been perfectly useful. Upon further research, the Monodactylidae I was considering stocking would best benefit from full strength sea water as adults (perhaps 12 months after introduction), so the salt consumption would go from about 500lbs in the first year to an annual 1000lbs (21x5g pails, or 2/month) with a trickle auto changer. It appears the brine would reduce the delivery system to 1.4g/day (or a 16% brine to fresh ratio) which is mechanically practical, but I'm going to re-assess the setup.. Perhaps dialing in to a monthly pail, reducing salinity and/or % change and introducing protein skimmers and more anoxic biological filtration. Thank you very much for your guidance!!