Reactors and Additives

[reefburnaby]

Hi,

I know some like to avoid the math and get to the practical stuff. I like to mix it a bit...mix some practical and get some theory down too.

I mentor a lot of engineers so I have to provide "proof" that I am not making things up. Which...usually means equations.....

- Victor.

[Canadian]

Just for the record:

"You do not really understand something unless you can explain it to your grandmother."

-Albert Einstein

And my grandmother isn't a chemist.

[DJ88]

Victor,

It is not that I want to avoid the math. As a technician I had to work with formulas all the time. Especially now.

It is that in this hobby the GAFF(Give A F*#k Factor) for chemical formulas and such is very low. How many people honestly go that indepth with this hobby. With regards to chemical intereactions. If I can explain it in such a way that everyone including myself can understand it then I am doing those out there reading a big favor. When people see those formulas they roll thier eyes and scroll down probably 90% of the time. I do. If I really wanted I can sit down adn research it to undersatnd all of it. But why? If you like to at home, great. Kudos for you. We aren't chemists, and most here aren't engineers. I'll gurantee you that there are people on this board who won't participate in these discussions as they are intimidated or can't understand the first thing about chemical interactions down to the molecular level. I last took Chemistry in high school. 15 years ago. I am sure there are others who didn't even take chem as they had something else they were more interested in.

With that said, I still think your reactor is not running right. It isn't a matter of plumbing, you need to slow the effluent rate to decrease the pH so that you are actually using your reactor for something more than a water circulation device.

I'll let this be now. Maybe you will take the advice and experience being offered and follow it. Maybe you won't. Your choice. But I know that if you don't you will still be adding buiffer to your tank for a looong loong time. And once you try putting more of a Ca demand on your system to the point that it starts falling too you will need to add Ca as well. Then what is the point of even running a reactor if you are dosing as well??

Hmmmm???

[Acro]

Andrew,
I would have to go on the show Crossing Over in hopes to explain it to my grandmother. j/k ] [img]images/smiles/icon_wink.gif[/img]
Victor,in all seriuosness you don't need to get to complicated about things. Bottom line... Ask yourself why you have a reactor in the first place.

[ 30 January 2002: Message edited by: Jamie Cross ]</p>

[Aquattro]

Just in case this helps anyone, here is an excerpt from Sanjay Joshi's paper.

"There are basically two adjustments that can be made to an operational reactor — the effluent flow rate and the amount of CO2 added. In the steady state, the trick is to balance the output of the reactor with the daily consumption of alkalinity in the tank.

Increasing the CO2, while maintaining the effluent flow rate, results in a decrease in the pH of the reactor and hence an increase in the solubility of the CaCO3 media, and hence a higher alkalinity in the effluent. This increase in alkalinity of the effluent will be seen up to a pH range of 6.3 to 6.5 and any further decrease of the pH in the reactor will start resulting in decreasing alkalinity. Increasing the effluent flow rate, while maintaining a fixed amount of CO2 will result in an increase in pH in the reactor and hence a reduction in the alkalinity of the effluent. By adjusting both the effluent flow rate and the CO2 injection rate, a fixed pH can also be maintained in the effluent. Some advocate maintaining a fixed pH of around 6.5 in the reactor.

I find it much easier to adjust the reactor based on the alkalinity output rather than the pH measurement. I would recommend first setting up an effluent flow rate so it flows in a continuous steady drip, and then making adjustments to the CO2 flow rate to increase or decrease the alkalinity of the output. For most tanks this approach will work fine, but if you have a heavily loaded small-polyped scleractinian (SPS) coral tank, then it may require you to increase both the effluent flow rate and the CO2 injection rate. A certain amount of fine-tuning is required to adjust the reactor for your particular system.

Having a good estimate of the daily consumption of the alkalinity in the tank and understanding some of the “reactor math” can help in eliminating some of the trial and error in fine-tuning the reactor. Let us assume that the reef system contains T liters of water, and the effluent flow rate is L liters per hour and the estimated daily alkalinity consumption is c milliequivalents per liter (mEq/L) per day. Now, measure the alkalinity in the tank and the alkalinity of the effluent. The difference between the two values will give you the increase in alkalinity due to the reactor — call this d (mEq/L) — as follows:

alk/day added due to the reactor = (d x L x 24)/T Equation 1

So, now we need to adjust the reactor so that the daily increase due to the reactor is approximately c mEq/L. This will give us the setting at which the reactor will replenish the alkalinity that is consumed daily.

Looking at the Equation 1, we can see that there are three ways this can be achieved:
Only adjusting d — the increase in effluent alkalinity
Only adjusting L — effluent flow rate
Adjusting both d and L.

The effluent alkalinity can be increased (or decreased) by correspondingly increasing (or decreasing) the amount of CO2 and keeping the effluent flow rate constant. This provides one convenient way of tuning the reactor output to the aquarium needs. When increasing the amount of CO2 added care must be taken to keep the pH level above approximately 6.3. I personally use this approach to adjust my reactor. If I find that I have to injected too much CO2 so as to cause the pH in the reactor to drop below 6.3, I am better off also increasing the effluent flow rate through the reactor.

Increasing the flow rate will result in a decrease in effluent alkalinity if the CO2 flow rate is not simultaneously increased. Several manufacturers recommend adjusting both the flow rate and the amount of CO2 simultaneously to maintain a constant pH (about 6.5) in the reactor and hence a constant alkalinity output in the effluent. I prefer having to just adjust one parameter — the CO2 flow rate. Both approaches will satisfy the needs of the user, but the key is to balance the daily consumption to the daily addition of alkalinity."

[StirCrazy]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by reefburnaby:
Hi,

kalk = Ca++ + 2 (OH2-)

CO2 when mixed in water becomes :

CO2 + H2O <=> H2CO3 <=> H+ + HCO3-

where H2CO3 is a carbonic acid and HCO3- is a bicarbonate. Okay...so, when the two mix...you get :

Ca++ + 2(OH-) + 2H+ + 2HCO3- <=> H2O + 2HCO3- + Ca-. So, the alk stays the same...but no more CO2 and one more Ca++.

- Victor.<hr></blockquote>

I do like chemical equasions but don'f forget Victor that the equasions you are using as a example are assuming all you have is "PURE water, PURE kalk, and C02". and all in exact ratios. we all know there are hundreds of other chemicals in the tank that will cause all new and exciting reactions to happen. so in all practicality it is ok to use the equasions to get a idea of what is going on but unless you want to do a studdy one every element in the tank and there ratios and then bring up the effect that motion of the elements and temp cause.. well you see I alreays would have packed it in [img]images/smiles/icon_smile.gif[/img] I love Chem but not that much

Steve

[Aquattro]

Steve, I saw that....

[Silverfish]

Well, alls I can say is .... tomorrow I pick up my 15lb co2 tank and I hope to soon say good-bye to that pesky dosing!!

[ldzielak]

These reaction formulae show the basics, but these are balanced equations, with no indicators as to what shifts the balance, temp? pH we all know does, this is how the reactor works right? When you change the CO2 flow and leave the rest, you change the balance. ARM says to set pH to 7.5 but if you read on the boards some say 6.5 the answer is find the balance for your systems demand and match the pH or output of the reactor.

Victor, how did you solve your valve pluging problem? I have to adjust my effluent needle valve every day or two.

[DJ88]

Lee,

I am running ARM in my reactor and have been keeping the pH at 6.9-7.0. I measured my alk today in my tank and it is still at 12 and my Ca is at 490. so you can run it higher than regular media. If you run it down near 6.5 it turns into soup. just so ya know. [img]images/smiles/icon_smile.gif[/img]