dangros January 7, 2015 Share January 7, 2015 So I was testing my Mg this week and was quite shocked to see that it was at 950ppm. The tank is a very new setup but cycled (2-3mos old). I had only done a couple small water changes but since I dont have any coraline or much in the tank other than dry rock and live sand, I wouldnt expect such a drop in Mg. Especially since Instant Ocean has 1264ppm. Since then, I started boosting it up w/Gary's DIY formula and it seems to be bouncing back as expected. Anyone have any idea what could be dropping it - or are my expectations off base w/a cycled tank and only a couple small water chgs in 2 months? Link to comment Share on other sites More sharing options...
bbyatv January 7, 2015 Share January 7, 2015 I would check your test kit. Maybe borrow a kit from another member and see what it reads. Bruce Link to comment Share on other sites More sharing options...
Origami January 7, 2015 Share January 7, 2015 Check the test kit, as Bruce mentions. Another way you can rapidly deplete magnesium is if you're running salt water through a kalk reactor (rather than fresh, top off water). In that scenario, the magnesium reacts with the hydroxide in the reactor to form magnesium hydroxide precipitate. Hopefully you're not doing that. Link to comment Share on other sites More sharing options...
dangros January 7, 2015 Author Share January 7, 2015 I'll chk the test kit but I have a feeling it's not that. Salifert tends to be right on and it's prob not a coincidence that my calc and alk were a little low also. I didnt use a kalk reactor, just the BRS mini reactor w/carbon and GFO. I also dripped Kalkwasser but w/RODI water. I'll make sure to test pure/new saltwater tonight. If that's as advertised, that should confirm that the kit is ok. If not, then it's either the kit or the salt. Link to comment Share on other sites More sharing options...
Origami January 7, 2015 Share January 7, 2015 (edited) How does your tank look? What's your salinity? How are you checking salinity? What numbers are you getting for Calcium and Alk? Another way to get low numbers is low salinity. The typical numbers we're looking for are for water at 35 pt (or 1.0264 sg). Low magnesium could also be the reason your calcium and alkalinity are low. Have you tried checking the magnesium in a freshly mixed batch of salt water? (Ignore that. You said you'd check tonight.) Edited January 7, 2015 by Origami Link to comment Share on other sites More sharing options...
dangros January 7, 2015 Author Share January 7, 2015 How does your tank look? It's got a black frame and clear glass all over There's a tiny bit of brown alg on the gravel but otherwise, looks quite nice now. What's your salinity? How are you checking salinity? What numbers are you getting for Calcium and Alk? Another way to get low numbers is low salinity. The typical numbers we're looking for are for water at 35 pt (or 1.0264 sg). Good questions, actually. My salinity was both high and low for a while but I corrected that this weekend. My Tunze auto topoff hose was submerged in the sump. So when the pump turned off, the water back siphoned back into the RODI reservoir. I didnt realize it till recently and fixed my stupidity. I've been keeping it at 1.025 but it got as high as 1.028 and low as 1.022 before I fixed the topoff. My shrimp didnt die so it couldnt have been too bad. That was scary though. I had nightmare visions of my floor getting soaked. Fortunately, that didnt happen. Link to comment Share on other sites More sharing options...
Origami January 7, 2015 Share January 7, 2015 Black frame - glass. That might be it. What are you using to check salinity? And is it calibrated? What numbers are you getting for calcium and alkalinity? Oh, and what salt are you using? (Instant Ocean from the first post.) A salinity of 1.022 is about 17% low. That would drop a mix that targets 1200 ppm of Mg to around 1000 ppm. If the numbers are all proportionally low, then it could just be a problem with salinity. Hard to say until you run a few more tests. Link to comment Share on other sites More sharing options...
AlanM January 8, 2015 Share January 8, 2015 My Mg numbers were high for a long time. I couldnt understand it because they were higher than reef crystals is even supposed to mix at. But then I got a new refractometer and discovered I was at 38ppt instead of 35. I even calibrated the old one, but the spring was broken inside of it and it would vary just by cleaning the calibration solution off a bit. Link to comment Share on other sites More sharing options...
zygote2k January 8, 2015 Share January 8, 2015 do regular w/c before dosing and see how stable your mg becomes. Link to comment Share on other sites More sharing options...
dangros January 8, 2015 Author Share January 8, 2015 (edited) Black frame - glass. That might be it. What are you using to check salinity? And is it calibrated? What numbers are you getting for calcium and alkalinity? Oh, and what salt are you using? (Instant Ocean from the first post.) A salinity of 1.022 is about 17% low. That would drop a mix that targets 1200 ppm of Mg to around 1000 ppm. If the numbers are all proportionally low, then it could just be a problem with salinity. Hard to say until you run a few more tests. I dont think 1.022 is 17% low. I recall that 1.023 was within the range of acceptable. Having said that, 1.025 seems to be the recommended level. My RODI unit is in in the garage. So eventhough there are heaters in the trashcans containing the salt mix, I have, at times, measured the salinity in the cold b/f heating the water! Here's something REALLY interesting that I just found: the density of seawater (S = 35) changes from 1.028 g/cm3 at 3.98 °C to 1.025 g/cm3 at 20 °C to 1.023 g/cm3 at a typical marine aquarium temperature of 80 °F. Since the density of the sample is changing with temperature, the measured specific gravity will also change, unless this is taken into account. Edited January 8, 2015 by dangros Link to comment Share on other sites More sharing options...
dangros January 8, 2015 Author Share January 8, 2015 I tested the water last night 2x. The first time, the Mg came out to a shockingly low 1100 ppm. So I checked the salinity with both the refractometer and the ole swing arm made by Instant Ocean. The io hydrometer measured the water at 2 g/cm lower than the refractometer. The thing w/the refractometer is that it's quite old. I dont know if that matters. It's also VERY hard to read due to the very small labels and my lack of 20/20 vision (dont get older people!) So I decided to pump up the salinity to 1.025 by measure of the supposedly less accurate swing arm and sure enough, the Mg tested at approx 1235. MUCH BETTER! So i suspect that the old refractometer is either inaccurate or too difficult to read/calibrate due to the ridiculously crowded tick marks and labels. I'm going to get a new one. Do any of you recommend one that is very easy to read? I took a look at the red sea one and it seems like it solves the prob I'm having. Note the Red Sea’s Refractometer display section: http://www.redseafish.com/red-sea-salts/seawater-refractometer-salinity-test/If you recommend a better/easier to read brand, please speak up! Link to comment Share on other sites More sharing options...
Wolf_Zero January 8, 2015 Share January 8, 2015 It's a bit of an expensive option by comparison, but the Milwaukee digital refractometer is probably one of the easiest to read. Link to comment Share on other sites More sharing options...
Origami January 8, 2015 Share January 8, 2015 I dont think 1.022 is 17% low. I recall that 1.023 was within the range of acceptable. Having said that, 1.025 seems to be the recommended level. My RODI unit is in in the garage. So eventhough there are heaters in the trashcans containing the salt mix, I have, at times, measured the salinity in the cold b/f heating the water! Here's something REALLY interesting that I just found: the density of seawater (S = 35) changes from 1.028 g/cm3 at 3.98 °C to 1.025 g/cm3 at 20 °C to 1.023 g/cm3 at a typical marine aquarium temperature of 80 °F. Since the density of the sample is changing with temperature, the measured specific gravity will also change, unless this is taken into account. 1.022 is 17% low of 35 ppt or 1.0264 sg, where a lot of reefing salt's parameters are measured. Anyway, it's important to know what a brand of salt is going to give you and at what salinity that's being quoted at. For example, a lot of the recordkeeping that was kept over at Reef Central on various salts was characterized at 35 ppt. That's what I meant by 17% low. Keep in mind that there are a bunch of ways to discuss this 35 ppt is salinity in parts per thousand - grams of salt in a kg of salt water. 1.0264 is specific gravity - this is a mass ratio that compares the mass of a substance with an equal volume of its standard. In this case, this refers to a the mass of a volume of salt water as compared to the mass of the same volume of fresh water at 4 degrees C and at 1 atmosphere of pressure. It's dimensionless. Then there's density - the mass of a certain volume of the substance normalized to volume. Example: grams per cc. And, it changes with temperature when the substance expands or contracts. This is why ice floats, for example. Each is different. Water expands, ever so slightly, when heated and still in liquid state. For example, a cc of liquid fresh water at 4 degrees C has 1 gram of mass. A cc of the same fresh water at 25 degrees C has 0.997 grams of mass. Another way of thinking about it is that if you heated a cc of water from 4 degrees C to 25 degrees C, it would expand from 1 cc to 1.003 cc in volume. This expansion changes the density. The same thing happens in our tanks, but the change is really small. Yeah, it can be confusing. But, the good news is, find a good measurement tool and stick with it. Strive for consistency (stability), not necessarily absolute accuracy. Now, on to your refractometer readings: First, many refractometers today have eyepieces that turn and adjust to our vision problems. I'm in my mid-50's and am presbyopic, so too late on the "don't get older" advice. (Also recently diagnosed with glaucoma, so I've got my first persistent (what I call "old people" - without offense, hopefully) prescription. LOL. Anyway, the thing that I find more important is to have some calibration fluid handy to calibrate your instruments, including a refractometer. If it's not calibrated, you can't trust it. If it can't hold calibration over the short term, toss it. Even a cheaper saline refractometer works well enough for our use, but you can get some good ones out there - for example H 2 Ocean D-D makes one. The other thing that I've found is to have a good, bright light source to use and to make sure that you have plenty of water under the viewing plate so there's a nice, consistent film underneath. If you're lacking either, the line gets fuzzy and is hard to read. I've got three refractometers and probably 3 or 4 swing arm hydrometers. The refractometers differ in quality but perform rather similarly. The hydrometers exhibit more measurement variation, but at least one of them gives me readings that are dead-on with two of my refractometers. Third, depending upon the type of refractometer that you're using (brine, salinity, sugar, wine, etc.), the scale could be way off. For example, all three of my refractometers have an SG scale on the left and a PPT scale on the right. However, one one, the 35 ppt lines up with 1.025 SG, not 1.0264 SG, where the other two line up. This goes directly to what it's measuring - salt water vice brine (NaCl + water). To adjust to the difference, I just pick what I want to measure, calibrate to it, and stick with it. In my case, I like to measure in PPT so I stick with reading that side of the scale on all my refractometers. Sorry for the long post. Your refractometer may still be good.Try calibrating it with some calibration fluid or asking your LFS to help you out with doing that. Link to comment Share on other sites More sharing options...
AlanM January 8, 2015 Share January 8, 2015 I like my new cheapish refractometer from BRS. Seems solid and temperature compensating and is easy to read. Link to comment Share on other sites More sharing options...
dangros January 9, 2015 Author Share January 9, 2015 Tom - I appreciate the long post so dont sweat it! Wolf - BRS had a nice special on the digital Milwaukee during the black friday time frame. I knew I would kick myself for not going for it but I was a bit shell shocked after jumping at the Vertex 150 skimmer. I really want one that is easier to read but in the meantime, I'm gonna wash my crappy IO old school hydrometer after every use and hope it does the job. The refractometer is going in the trash. So I measured everything again today and it seems to be a bit more inline with what I would expect. The results: Mg - 1260 (keep in mind that I boosted it about 200ppm w/Gary's diy potion) Ca - 390 Alk 2.82 meq/l Salinity 1.0245 (was in between 1.024 and 1.025) Phosphates - 11 The phosphates are a little high but I am running GFO in the brs min reactor so hopefully that is gonna drop soon. After reading some posts, I suspect my BRS Pukani is leaching out some Phos. After measuring, I did a small water chg (approx 10g). I purposely mixed the water to 1.030 so that I would get the salinity up a tad in the tank and it worked perfectly. I will likely do another small water chg tomorrow. I think the reason things were out of wack was 3 fold: 1) my recraptometer was off (*and yes I did calibrate as instructed by the documentation using rodi water*) 2) as a result of #1, my salinity was too low causing my Mg to be lower 3) I needed to do more water chgs. Link to comment Share on other sites More sharing options...
Origami January 9, 2015 Share January 9, 2015 The numbers are sounding better. Keep in mind that brine refractometers may not really be able to be calibrated with RO/DI. (That's why It's my standard practice to calibrate all refractometers using calibration fluid specifically made for refractometers.) Here's a little something on the H2Ocean DD refractometer. The introductory paragraph gives you some idea of how the printed scales - not the physical principle behind refraction - can screw up your reading. A good article here, too. Another favorite of mine is here. Link to comment Share on other sites More sharing options...
DuffyGeos January 9, 2015 Share January 9, 2015 I use this one. It has a larger scale so it is easier to read. Buy the cal. fluid with it. $65.00+/- http://www.marinedepot.com/Marine_Depot_Aquarium_Pro_Refractometer_Aquarium_Refractometers-Marine_Depot-MD2103-FITEOPRF-vi.html Link to comment Share on other sites More sharing options...
Origami January 9, 2015 Share January 9, 2015 I use this one. It has a larger scale so it is easier to read. Buy the cal. fluid with it. $65.00+/- http://www.marinedepot.com/Marine_Depot_Aquarium_Pro_Refractometer_Aquarium_Refractometers-Marine_Depot-MD2103-FITEOPRF-vi.html This is one of my three. Of the three, I probably like it best. Link to comment Share on other sites More sharing options...
DuffyGeos January 9, 2015 Share January 9, 2015 This is one of my three. Of the three, I probably like it best. But you have always has good taste! Link to comment Share on other sites More sharing options...
dangros January 9, 2015 Author Share January 9, 2015 awesome. that's what I'm looking for - stable, easy to read instrument! Thanks guys! I noticed the marine depot one measures at 20C. Is that the temp of the refractometer or the water it's measuring? I guess it doesnt really matter b/c once those few drops of water sit for a few seconds, they will pretty much be at room temp. Link to comment Share on other sites More sharing options...
DuffyGeos January 9, 2015 Share January 9, 2015 awesome. that's what I'm looking for - stable, easy to read instrument! Thanks guys! I noticed the marine depot one measures at 20C. Is that the temp of the refractometer or the water it's measuring? I guess it doesnt really matter b/c once those few drops of water sit for a few seconds, they will pretty much be at room temp. I keep the refractometer room temp, drip a few drops, then let it sit for a few min. Which is what they say to do. Make sure to order the calibration packs, it does not come with it and you need it to zero it out. You can also adjust the focus on lens for your eyes. A good refractometer adjusted correctly is tons more accurate then the old IO swing arm ( mine was used from 2004- 2007) I think I threw mine away after seeing the difference in the readings ( checked it with another refractometer). My Salinity was probably 1.022 instead of 1.025, things started to look better in my tank after that. Link to comment Share on other sites More sharing options...
Origami January 9, 2015 Share January 9, 2015 Many, including the Marine Depot refractometer, are temperature compensating (they'll often say ATC, which stands for automatic temperature compensation). The 20 degrees C is 68 degrees F, or about room temperature. Around this temperature, the performance may vary a little bit, but because of the ATC, it shouldn't be too much. Link to comment Share on other sites More sharing options...
dangros January 10, 2015 Author Share January 10, 2015 interestingly, the Red Sea refr. has all the traits of the Marine Depot Pro but it's calibrated to 77F vs 68F. That seems like it would be a little more convenient as long as you measured right away w/o allowing the water sample to cool too much. It's a difficult choice, at least on paper! Link to comment Share on other sites More sharing options...
AlanM January 10, 2015 Share January 10, 2015 I hardly measure tank water. Normally new saltwater that I am mixing up. That is more likely to be lower temp. Link to comment Share on other sites More sharing options...
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