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Old 03/31/2003, 09:05 AM
Randy Holmes-Farley Randy Holmes-Farley is offline
Reef Chemist
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 52,068
Wfere to ask me chemistry questions

If you are interested in getting answers to most any reef tank chemistry questions, you should post the question in my reef chemistry forum here at Reef Central:

The forum that you are presently in is for questions directly relating to my articles at If I don't have any recent articles, I often don't check here for substantial periods, but I check the other forum daily.

Happy Reefing!
Randy Holmes-Farley
Old 10/06/2003, 10:40 AM
Dr Greg Alexander Dr Greg Alexander is offline
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Join Date: Oct 2003
Posts: 8
Ive read your Ca/ Alk articles. I am currently in zone 2. Salifert ALK reading is 8.22. My Ca is 420, after being in Zone 3 . Ive shut off my Ca/CO2 reactor., and assume I just wait . Am I correct?

Greg K. Alexander
GkAlex DC Houston
Old 10/06/2003, 11:05 AM
Randy Holmes-Farley Randy Holmes-Farley is offline
Reef Chemist
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 52,068
Salifert ALK reading is 8.22.

8.22 meq/L or 8.22 dKH?
Randy Holmes-Farley
Old 11/10/2004, 08:04 PM
fio1022 fio1022 is offline
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Join Date: May 2004
Location: Wantagh,Long Island
Posts: 860
Hi Randy,
I've been using a TDS to monitor my D.I. unit to determine when to regenerate the resins.I'm getting a reading that varies btwn 4-6 ppm.At what point should I regenerate?
Thanks for all your valuable wisdom.
its all about time,space,and money
Old 11/10/2004, 09:51 PM
Randy Holmes-Farley Randy Holmes-Farley is offline
Reef Chemist
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 52,068
Did it start lower? Most DI units should give 0-1 ppm when workign well, as as the TDS rises when the get shot, things go bad fast.

You might check this article:

What is TDS?

from it:

"7. If you are using a TDS or conductivity meter to monitor the performance of an RO membrane, then the measured value should drop by at least a factor of 10 from the starting tap water. So, for example, if the tap water reads 231 ppm, then the RO water should be less than 23 ppm. In many cases, it will drop much more than that. Less of a drop than a factor of 10 indicates a problem with the RO membrane.

8. If you are using a TDS or conductivity meter to monitor the performance of an RO/DI system, then the measured value should drop to near zero. Maybe 0-1 ppm. Higher values indicate that something is not functioning properly, or that the DI resin is becoming saturated and needs replacement. However, that does not necessarily mean that 2 ppm water is not OK to use. But beware that it may begin to rise fairly sharply when the resin becomes saturated. Do not agonize over 1 ppm vs. zero ppm. While pure water has a TDS well below 1 ppm, uncertainties from carbon dioxide in the air (which gets into the water and ionizes to provide some conductivity) and the TDS meter itself may yield results of 1 or 2 ppm even from pure water. "
Randy Holmes-Farley
Old 04/08/2005, 03:04 PM
aka_BigRed aka_BigRed is offline
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Join Date: Mar 2004
Location: St. Paul, MN
Posts: 162
I have a question about ion-selective probes (calcium from your recent article in Reefkeeping) and their raw output.

I'm working on a project to develop a DIY reef controller and I'd thought about adding a Ca probe to monitor Ca levels. From your article, the electrode puts out a variable milivolt reading based on the concentration of Ca, but do you know where I could find out the conversion factor from mV to PPM concentration? Is it a direct relationship or log scale or some strange equation? I'm having a tough time finding out the conversion factor/equation that the meters use. I also had the same question for a Nitrate probe.

Adding ORP should be easy since the readings and standard units people use are just plain milivolts. I just can't get info on the output conversion scale for other "fun" probes.

Old 01/04/2006, 02:56 PM
Randy Holmes-Farley Randy Holmes-Farley is offline
Reef Chemist
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 52,068
I presume that this got answered in my other forum?
Randy Holmes-Farley
Old 02/05/2007, 10:53 PM
glanka glanka is offline
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Join Date: Oct 2006
Posts: 1
Degradation of kalkwasser article

Hello Randy
I am from melbourne and have a 4 month old 180 liter reef tank.
This my first posting and hope i got it right.
Your articles are much valued and thank you.

I make kalk from ca(oH)2 powder in a 40liter trash bin. As suggested in your article you fill the trash can once in 2-3 weeks.
When and how do you add ca(OH)2, and or remove the exisiting sludge that has settled at the bottom of the trash can ?
In other words how often do you remove the sludge and add the new Ca(OH)2?.
Than you for the advice
Old 02/06/2007, 04:57 PM
Randy Holmes-Farley Randy Holmes-Farley is offline
Reef Chemist
Join Date: Apr 2001
Location: Arlington, Massachusetts
Posts: 52,068

This is an OK place to ask, but the chemistry forum is better:

I do not remove the sludge very often (once a year maybe). I usually add new calcium hydroxide whenever I refill it with water (I now use 2 x 44 gallon trash cans connected together). Sometimes i try to get more out of the sludge and don't refill with calcium hydroxide, but I always check the conductivity to make sure the potency is adequate.
Randy Holmes-Farley
Old 05/08/2007, 09:23 AM
reefscapes4u reefscapes4u is offline
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Join Date: Sep 2006
Posts: 6
toxic dinos

Dr Holmes-Farley

Hello and first let me say how helpful your articles on reef chemistry have been. I've been in the hobby for 15 years and have learned more in the last year from reading your articles than in the rest combined. Its good to hear solid answers about alot of things that are often misconstrued in this hobby. I am writing today to try to get some answers on a very unusual problem i have been having with some of the tanks i maintain. Out of all the research i have done you are the only person who seems to have heard of this problem. I have been killing fish when i scrub troublesome algae off the sides of these tanks. I thought it was contamination with my equipment for the longest time. After taking a sample of this stuff to a veteran biologist up at CSU he identified it to me as Amphidinium Carterae a toxic Dinoflagellate that is capable of producing neurotoxins. I found your article on dinos doing a search and found that they don't like elevated Ph. I dosed numerous Kalk slurries, covered tank, and turned light off. I also did vigorous nutrient export using pura phoslock, polyfilters, and chemi-clean. it seemed to have worked for awhile however now with lights on and Ph back to normal its coming back. All water parameters check out well alk 3-4 meg/l cal 350-380 and Phosphate less than .03 yet this stuff still grows. It is dark brown in color and if let to grow for awhile will develop small hairlike structures on it. Coral and Coralline all do well. it only affects the fish which will go into shock breathing rapidly and darting around soon dying of asphyxiation if alot of this stuff gets into the water column. I desperately want to get rid of this stuff and cant believe that i am the first to ever encounter such a thing. I am hoping that you have heard of others having such problems and would love to hear some success stories on how they managed to eradicate this stuff. Any info or links you may have would be greatly appreciated. If you need more info or some pictures of this stuff i would gladly forward them to you. i have posted numerous threads on reef central but nobody seems to know what I'm talking about. I apologize for tracking you down like this but i am very eager to get some professional answers. Thanks in advance for your help.


Justin Erwin
Reefscapes Service Co
6489 S Xenophon St
Littleton, CO 80127
Old 08/08/2007, 04:35 PM
nrehman nrehman is offline
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Join Date: Feb 2006
Location: Washington, DC
Posts: 50

(This post may be in the wrong location).

Not a question, but a THANKS. What a great way to teach/learn with the chemistry quiz.
Old 12/07/2007, 02:35 PM
SCIFI_3D_zoo SCIFI_3D_zoo is offline
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Join Date: Nov 2005
Location: Florida
Posts: 222
Great resource your article.

I'm debating with somebody about IODINE. I read your article but I know what this guys comeback is gonna be. There are certain creatures that need IODINE like shrimp so they can molt, clams I thought, etc.

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