High Alkalinity

[Ninong]

"In typical marine aquarium practice, salinity is measured as specific gravity (sg). The proper salinity range for a marine aquarium measured in specific gravity units is 1.020 to 1.026. The true specific gravity of seawater at 35 ppt is 1.026." "Reef tank systems with live corals should be operated at near normal salinities of 33 to 35 ppt". The Marine Aquarium Reference, Martin Moe 1989.

I think that's because twenty years ago they typically used hydrometers to measure specific gravity as an indirect way of estimating salinity. I certainly agree with Moe's recommendation of 33 to 35 ppt salinity for a reef aquarium but I believe his range of 1.020 to 1.026 specific gravity (27 to 35 ppt) for a marine aquarium is a little wide. I think a better range, when measured in specific gravity, would be 1.023 to 1.026.

This was my first real book I bought in 1989 and as such I became habituated using sg. It is still today the most common reference to salinity used, although not as much as 20 years ago.

I'm sure everything he recommended twenty years ago still holds true today but I believe there is no real benefit to keeping reef fish at unnaturally low salinity for extended periods. In my opinion, the idea that lower salinity is easier on the fish because they have to use less energy for osmotic regulation is misguided. Lower salinity probably leads to shortened lifespans due to premature kidney failure. Lower salinity is popular in the trade because it saves on the cost of salt mix.

I use a cheap hobbyist refractometer calibrated to DI water and then add .001 sg. so I'm really getting 34.3 ppt. Although it's not exact I don't think it really makes that much difference overall and probably within the repeatability of most hobbyist test kits which range plus or minus 10-20ppm. I will mix up some at the slightly higher salinity today and report back the new readings.

That's the point I was trying to bring up. You and Charlie posted chemical analyses but at different specific gravities and then there was the posibility that you guys were using different methods to measure the specific gravity.

If we want to see if Instant Ocean and Reef Crystals truly have been improved, as claimed, we should test them at 35 ppt (1.0264 SG).

One other note. I checked the buckets of IO and they don't recommend a certain salinity level or make any claims about specific mineral content.

They have never printed claims for mineral content on their packaging but they used to print a recommended specific gravity that was much lower than what Charlie said they are now recommending. I wonder why they would not make any recommendation at all about salinity (specific gravity), especially now that they claim to have boosted their mineral content so that it measures better at higher specific gravity than they used to recommend?

Instant Ocean's website still has the same Saltwater Manual that claims that most hobbyists use a cheapy hydrometer, such as their Instant Ocean hydrometer, to measure specific gravity. "In actual practice, most hobbyists dispense with the use of salinity and simply refer to the specific gravity. The range of 1.020 to 1.023 is most common."

That advice is on page 10. On page 9 they tell you that "Normal seawater salinity is 35 parts per thousand, meaning that 1,000 grams of seawater contains 35 grams of dissolved salts."

Instant Ocean: The Seawater Manual

On page 23 they tell you that "Temperatures of 70 to 80 degrees Fahrenheit are ideal." I don't know where they got the idea that 70 degrees was "ideal" for a tropical reef aquarium. That's ridiculous!

They go on to say that "Ideal salinities are 27 to 35 parts per thousand, which correspond to specific gravities of approximately 1.020 to 1.026." The lower end of that range is really unnatural for a reef aquarium or a marine aquarium with typical tropical reef fishes.

On their bags and buckets of Instant Ocean salt mix -- which I haven't looked at in at least four or five years -- they used to tell you how many cups of salt mix to use per gallon of tapwater to achieve a specific gravity of 1.021 or 1.022 (something like that). I can't remember the exact specific gravity number, I just remember that it wasn't 1.025 or 1.026. It was much lower than what Charlie says they are now recommending.

What that means is that a 50-gal bag of I.O. salt mix did not make 50 gallons of saltwater if you wanted to mix to a salinity of 35 ppt (1.0264 SG). To achieve natural salinity, you had to use more salt mix than they recommended in the instructions printed on the bag.

[charlie]

Kevin and Charlie,

How are you guys measuring specific gravity? Are you using a refractometer?

And, second, why are you both reporting specific gravity instead of salinity? Wouldn't it make a lot more sense to report salinity as salinity?

I use a refractometer George. I report specific gravity, because that is always the way I have done things. It may make more sense to you to report as salinity, but if you can equate the 2 what difference does it really make???

[Doodaa]

wow, now that we are talking about salinity and specific gravity....I know there is a multiplier to convert the two. I am now questioning if specific gravity and salinity is truly the same thing (take into account the multiplier).

I'm maybe thinking to deep, but are there any additives that would increase specific gravity as measured with a calibrated swing arm jobby and not increase the salinity/specific gravity as measured in a refractometer? The refractometer I use has two scales, specific gravity and salinity.

[Ninong]

I use a refractometer George. I report specific gravity, because that is always the way I have done things. It may make more sense to you to report as salinity, but if you can equate the 2 what difference does it really make???

The specific gravity reading on your refractometer is not accurate if your refractometer is calibrated with distilled water equalling zero. It's a brine refractometer, not a seawater refractometer.

The point is that everybody is reporting different numbers using different pieces of equipment and none of the numbers are comparable because no one knows what they really represent.

If we want to verify the claims that Aquarium Systems is making for Instant Ocean and Reef Crystals at 35 ppt, then we have to make sure that we are mixing the saltwater to a true 35 ppt. That's all. Oh, plus the other point that specific gravity is not salinity.

[Ninong]

The refractometer I use has two scales, specific gravity and salinity.

If you have a refractometer, read the salinity scale and ignore the specific gravity scale.

If your refractometer reads zero with distilled water, then when it reads 35 ppt salinity that means that your salinity is really 33.3 ppt. That's because these are all NaCl refractometers, not seawater refractometers. The refractive index of NaCl at 35 ppt is the same as the refractive index of seawater at 33.3 ppt.

There is nothing wrong with your refractometer. It's a perfectly fine refractometer and will do very nicely. All you have to do is remember that if you want your salinity to be approximately the same as natural seawater, then shoot for a reading between the 36 ppt and the 37 ppt lines on the scale. Or just shoot for a reading of 36 ppt and that will give you a salinity just slightly less than NSW.

Read Randy's article if you want a detailed explanation.

Reference: Randy Holmes-Farley.

[kevinpo]

Here are the numbers I got after mixing 100 gallons of IO at 35 ppt. I keep 100 gallons at the ready and I used 90 gallons of the last batch I tested. So I grabbed two more bags from the same box (each box contains 4 bags that mix about 50 gallons each).

Alkalinity 10.2 dKH
Calcium 375ppm
Magnesium 1170ppm

I don't think that the variation is due to testing methods but rather variation in the salt mix. I perform many more tests per week than the average hobbyist.

Regards,
Kevin

[CutthroatKid]

I didn't leave, I've still been reading your guys posts and learning stuff.

I tested my tank... 15-16dKH
So I'll get some salt mixed up and just test that. I forgot to in last WC...

Kevin, I'm headed for Seattle tomorrow morning. If it is the salt, should I try bring it?

[kevinpo]

Hello,
Sorry I missed your post. We have had a few lighting storms and they keep knocking out my Internet for a time. If you are in the area you can bring it by.

Regards,
Kevin

[returnofsid]

Wow Kevin, a few lighting storms is right!! That one we had Friday night was one of the most intense I've seen in many years. Up here, in our part of town, it was incredible. I stood out on the porch and watched 6" of water fun down our street...lol. Lightning bolts and Thunder claps were simultaneous!! Now back to the Alk thread!! Sorry all!!

[CutthroatKid]

I've never seen as many dust devils as I did out by you guys. it was crazy.
Kevin thank you for that, but now I'm back home. I tried to see if you were around the store yesterday, but you must have had better things to do on the day off ;)

As for Alk, I am thoroughly confused. I tested Wednesday before I left and got a Dkh of 16... today it is 13 and nothing has changed.
Is there a chance the flake food I use occasionally changes it? the person I left in charge only fed frozen food once a day. I usually feed the fish a little flake in the morning, then a frozen meal in the evening. I only feed a tiny amount of flake though, and 99% of it is eaten. That's the only thing I can think of...

[kevinpo]

Hello,
Sorry I missed you.

I tested Wednesday before I left and got a Dkh of 16... today it is 13 and nothing has changed.

Your tank alkalinity should continually drop as corals and coralline algae deplete it. The things that can make it rise are:
Water changes (salt mix).
Using tap water for evaporation (Ground water can contain high levels of minerals depending on where you live).
Adding Kalkwasser (calcium hydroxide).
Adding buffer (sodium bicarbonate, sodium carbonate.

Regards,
Kevin

[CutthroatKid]

Thanks Kevin. I guess I didn't think about it, but I should've known corals would lower it. I guess I'll get the second bucket checked and go from there. they are different numbers by the way...