Crystalizing 3-Part Dosing Alk Line

Darth_Tater · 02/15/2019, 09:40 PM

So I've got my dosing pump lines sitting in a probe holder so that the ends are about 2 inches above the water line in my sump. The lines are all at least an inch apart. The Alk line keeps building up crystals on the end of the hose that eventually block it. There's not a lot of splashing to create salt spray on the line, and the lines are far enough apart there's no cross-contamination between them.

I haven't had any major issues yet, but it's just a matter of time. Any suggestions?

windlasher · 02/15/2019, 10:05 PM

Quote:

Originally Posted by Darth_Tater

So I've got my dosing pump lines sitting in a probe holder so that the ends are about 2 inches above the water line in my sump. The lines are all at least an inch apart. The Alk line keeps building up crystals on the end of the hose that eventually block it. There's not a lot of splashing to create salt spray on the line, and the lines are far enough apart there's no cross-contamination between them.

I haven't had any major issues yet, but it's just a matter of time. Any suggestions?

I have that too. Will be following.

dkeller_nc · 02/17/2019, 07:59 AM

One aspect of this that you may have already realized if you DIY your 3-part solutions is that a sodium bicarbonate (or sodium carbonate) solution when made up to the concentration typically used are very nearly saturated. That means that any evaporation at the tip of your dispenser is going to lead to crystallization.

There's several potential fixes. One is to make up the NaHCO3/Na2CO3 solution a bit more dilute than is typical, and simply up the dosing amount to compensate. Diluting it by 10% or so should be enough.

Another potential fix is to make sure that the cabinet underneath the tank stays closed to ensure high humidity, since reducing evaporation at the dispense tip will slow down crystallization.

Finally, since typical alk solutions are near saturation, and degree of saturation is a function of temperature (higher temps will dissolve more NaHCO3/Na2CO3), you could move your dosing container outside of the cabinet/sump. Presuming that your house temperature is a good bit lower than your reef tank's temperature, crystallization will occur in the dosing container rather than at the dispense tip.

One note about this. Depending on what sort of chemistry parameters you run, it might be possible that what you interpret as crystallization of sodium bicarbonate at the dispense tip isn't. Instead, it's actual formation of calcium carbonate from the reaction of the carbonate/bicarbonate with calcium in your tank water (even though the tip's above the water, there's still splashing/spray to consider). Fortunately, that's an easy test - scrape some of the crystals off of the line, and put them in tap water. If they dissolve, then it is indeed precipitation of the alkalinity reagent. OTOH, calcium carbonate will not dissolve in just about any amount of tap water. If you want further confirmation, simply add a few drops of acid to the test mixture. If the crystals won't dissolve in tap water, but quickly dissolve after a few drops of vinegar, then it's definitely calcium carbonate.

pscheel · 02/17/2019, 08:19 AM

Try cutting the end of the tube at an angle to see if that helps. If you have an ATO you can place ATO tubing above the the probe holder to rinse it off when it fills your sump. That is what I do and it keeps it nice and clean.

Darth_Tater · 02/17/2019, 08:58 AM

Wow dkeller, thanks for the explanation! It makes perfect sense. I bet it is from evaporation. Didn't even consider that.

Quote:

Originally Posted by pscheel

If you have an ATO you can place ATO tubing above the the probe holder to rinse it off when it fills your sump. That is what I do and it keeps it nice and clean.

This is a great idea as well. I'll have to see if I can wrestle the ATO line into a different place. Thanks!

jjencek · 02/18/2019, 02:32 AM

How about just leaving the end of the tube under water instead of above the surface?

dkeller_nc · 02/18/2019, 08:48 AM

Quote:

Originally Posted by jjencek

How about just leaving the end of the tube under water instead of above the surface?

A couple of issues with doing that. Potentially, that could actually start a siphon from the dosing container into the tank (which would cause a huge spike in alkalinity). The second issue is that most alkalinity solutions are concentrated enough that they'd react with the calcium in the saltwater diffusing into the alk tube to cause a blockage with precipitated calcium carbonate.

homer1475 · 02/18/2019, 11:58 AM

Quote:

Originally Posted by pscheel

If you have an ATO you can place ATO tubing above the the probe holder to rinse it off when it fills your sump. That is what I do and it keeps it nice and clean.

+1

I do this exact same thing and have not had a problem in 3 years since I started doing it this way.

02/15/2019, 09:40 PM	#1
Darth_Tater Registered Member Join Date: Feb 2015 Location: Northern Utah Posts: 535	Crystalizing 3-Part Dosing Alk Line So I've got my dosing pump lines sitting in a probe holder so that the ends are about 2 inches above the water line in my sump. The lines are all at least an inch apart. The Alk line keeps building up crystals on the end of the hose that eventually block it. There's not a lot of splashing to create salt spray on the line, and the lines are far enough apart there's no cross-contamination between them. I haven't had any major issues yet, but it's just a matter of time. Any suggestions? __________________ It's probably in your best interest to ignore most of my advice.

02/17/2019, 08:19 AM	#4
pscheel Registered Member Join Date: Feb 2000 Location: Chicago, IL Posts: 889	Try cutting the end of the tube at an angle to see if that helps. If you have an ATO you can place ATO tubing above the the probe holder to rinse it off when it fills your sump. That is what I do and it keeps it nice and clean. __________________ Pete Current Tank Info: 90 Gallon

02/17/2019, 07:59 AM	#3
dkeller_nc Registered Member Join Date: Mar 2013 Location: Central NC Posts: 5,062	One aspect of this that you may have already realized if you DIY your 3-part solutions is that a sodium bicarbonate (or sodium carbonate) solution when made up to the concentration typically used are very nearly saturated. That means that any evaporation at the tip of your dispenser is going to lead to crystallization. There's several potential fixes. One is to make up the NaHCO3/Na2CO3 solution a bit more dilute than is typical, and simply up the dosing amount to compensate. Diluting it by 10% or so should be enough. Another potential fix is to make sure that the cabinet underneath the tank stays closed to ensure high humidity, since reducing evaporation at the dispense tip will slow down crystallization. Finally, since typical alk solutions are near saturation, and degree of saturation is a function of temperature (higher temps will dissolve more NaHCO3/Na2CO3), you could move your dosing container outside of the cabinet/sump. Presuming that your house temperature is a good bit lower than your reef tank's temperature, crystallization will occur in the dosing container rather than at the dispense tip. One note about this. Depending on what sort of chemistry parameters you run, it might be possible that what you interpret as crystallization of sodium bicarbonate at the dispense tip isn't. Instead, it's actual formation of calcium carbonate from the reaction of the carbonate/bicarbonate with calcium in your tank water (even though the tip's above the water, there's still splashing/spray to consider). Fortunately, that's an easy test - scrape some of the crystals off of the line, and put them in tap water. If they dissolve, then it is indeed precipitation of the alkalinity reagent. OTOH, calcium carbonate will not dissolve in just about any amount of tap water. If you want further confirmation, simply add a few drops of acid to the test mixture. If the crystals won't dissolve in tap water, but quickly dissolve after a few drops of vinegar, then it's definitely calcium carbonate.

02/18/2019, 02:32 AM	#6
jjencek Registered Member Join Date: Dec 2016 Location: Prague, Czech Republic Posts: 366	How about just leaving the end of the tube under water instead of above the surface?