I can't keep my salinity down?

[BlackTip]

Salinity has been creeping up steadily due to high dosing of 2 parts. 528ml of soda ash and 528ml of ca daily. It is the only way to keep parameters stable.

I try to keep salinity at 33.3 ppt. It has been creeping to 34.6 ppt.

Total water volume is 350g

3 weeks ago, I replaced 5g with 5g of ro/di water, to knock it down .5ppt

Then, every water change I replace 25g with 29 ppt water to bring it down .5ppt.

Yesterday, I changed 30g water with 29 ppt, and still didn't bring it down.

I am using Milwakee refractometer and Neptune salinity probe. Both are calibrated and cleaned and read same numbers.

What could possible going on? I am nervous now that my salinity at the top end, and I am unable to bring it down slowly.

I use kalk water for top off, it it matters.

[thegrun]

35 ppt is really the ideal salinity, that said your salinity will continue to rise even if you kept it at 35ppt. I use a very wet skimmate to keep my salinity down but I have a big reservoir. Assuming you have a skimmer, I would look to add a remote skimmate reservoir and skim wet so your ATO is adding fresh water frequently.

[bertoni]

I agree that 35 psu (similar to 35 ppt) is the standard target. Kalk is fine for topoff, and it won't raise the salinity over time the way the 2-part will. How much is the salinity rising per week, without water changes? You might need to switch to a calcium reactor if you don't want to deal with this salinity change.

[BlackTip]

Thanks guys. I am putting a CR together right now. I hope I have it running in a week or so.

[bertoni]

Okay, that probably is the easiest way to deal with this situation.

[dkeller_nc]

To assist, I did a few calculations. Randy's Recipe #1 for calcium and alkalinity results in solutions that are about 0.94 moles/liter. Calculating the weight percentage, you get 100 grams per liter for the alkalinity part, and 104 grams per liter for the calcium part. So for our purposes I'm going to approximate both solutions at 100 grams/liter.

Since you're adding approximately 1060 mL/day to your system, and 350 gallons is 1325 liters, you're adding 0.08 grams of ionic solute per liter per day.

That's precisely equivalent to raising the apparent salinity 0.08 parts per thousand per day. Since you observed an increase of 1.3 ppt, that would take sixteen days, or about 2 weeks. In reality, it would take a bit longer assuming that you're pulling out skimmate, which is approximately the same concentration of dissolved ionic solutes as the tank water (i.e., 33 ppt)

Assuming you wanted to keep the salinity constant at 33 parts per thousand, then you'd need to remove 106 grams of dissolved solids per day. 33 ppt seawater has 33 grams of dissolved solids per liter, so you would need to remove 3.2 liters of tank water per day (and let the ATO make up the volume with RODI/kalkwasser). That's assuming that you didn't remove any skimmate, so you can reduce the required removal volume by the average skimmate collection volume on a one-to-one basis.

If you'd like to avoid the complexities and potential downsides of a calcium reactor, it would be pretty easy to use one of litermeter's auxillary peristaltic pumps with your controller to remove a little less than a gallon per day, and let your ATO make up the deficit.

[CStrickland]

When you're getting that much of your salinity from soda ash, is there a risk of becoming deficient in the other elements that a salt mix normally provides? Like since you're using that much less reef salt, are you getting that much less molybdenum, or unobtanium, or whatever? I can see that being an issue where a tank fails to thrive even with "good" water params since we don't test for those smaller stuffs.

[dkeller_nc]

No. In this case, his additions are actually a bit below what I might expect for an established tank with good coral growth - I dose double what BlackTip does on a per-gallon basis.

The main issue isn't trace elements, it's the skewing of the normal chloride to sulfate ratio in seawater. As 2-part is dosed, the sulfate will be "depleted", assuming adjustments are made to the overall specific gravity. That's why Randy's recipes include a magnesium mix that is heavily skewed towards magnesium sulfate (approximately a 9:1 ratio). This extra sulfate re-balances the chloride:sulfate ratio.

However, since a lot of salt mixes have bumped their magnesium concentration up considerably over seawater's, and magnesium is consumed slowly, most find that magnesium additions are unwarranted.

So in that case you must rely on water changes to re-balance the chloride to sulfate ratio. The good news is that I've never seen a reliable report attributing a reef animal health issue to a moderately imbalanced chloride:sulfate ratio.

[bertoni]

Over time, the two-part will increase the concentration of sodium and chloride, and decrease the proportion of other elements, assuming no water changes and dilution to keep the salinity down. Any reasonably good water change schedule should be able to handle that swing, though.

[wayne in norway]

Without wishing to appear rude I'd likely disagree with that statement - there's a lot of Ca and alk going in without any additional trace elements, Mg, sulphate et al., and it would need to be one heck of a water change schedule to keep up, as well as the fact that he needs to remove elements in the daily water removal/skimmate to keep salinity down.

While they are comparatively 'real world' values to add, it is always worth stopping dosing for a day to see what the drop in parameters is. I would hate to be adding all that, only for most of it to be precipitated out, and straight out the skimmer as microparticles.

[dkeller_nc]

My reasoning has to do with the biology of trace element utilization. Typically, these elements are incorporated into enzymes, or is a co-factor for an enzymatic reaction, so they don't get "used up" the way carbon and calcium get consumed to build skeletons and other tissues.

As such, the concentration requirement for trace elements is typically much, much more flexible than it is for "major" components like calcium and alkalinity.

It's sort of like vitamins for humans - some is absolutely required, but an excess doesn't do anything (or may be harmful). That said, I'd think that some degree of water changing and/or analysis and supplementation (such as via the Triton method) would be helpful over the long term.

[bertoni]

I get about a 10% dilution steady state, assuming a 10% change every two weeks. I get about 5% for a 20% change every two weeks.

[Reefheart]

So in short, dose to avoid significant water changes to replenish minerals but to counter the salinity rise, one needs to do significant water changes with fresh water? :eek2::confused:

[dkeller_nc]

It isn't reasonable to do significant enough water changes to replace major/minor compounds, such as Ca, Alk, and Mg. Unless, of course, one is referring to a pico or nano reef. But even if one changes 100% of the water in such a reef once per week, the parameter fluctuations would be sufficient to probably preclude keeping sensitive specimens like Acros.

Trace elements are another matter, however. Generally speaking, these only need to be above "deficiency" levels, with the animals very insensitive to 2X or 4X of these concentrations.