View Full Version : Could a controller adjust ph via an algae scubber?

02-13-2010, 11:07 AM
I just purchased the digital aquatics reefkeeper lite basic,has addable ph controls, for $99 mainly because I have not heard

good things about aquarium heater on/off switches. I had a jbj temp controller on the way but for only

$10 difference this seemed to make more sense. ( upgradeable and more functions) The idea I am throwing

around is to use an overly powered led algae scrubber to adjust, via the controller, the PH. (well use just as a

temp controller at first and then work up to a real time PH indicator) As the scrubber runs, lights are on, CO2 is absorbed

and subsequently the ph rises. This will, I believe, mainly appeal to a FW mostly fish only tank. (assuming) My

thinking is if you have a overly powered algae scrubber that a good indication that the scrubber is working

would be an increase in PH. Might also avoid any burn of the algae because the adjustments would only be made

when needed and the would never dip so far one way or the other because of the controller. Several ? arise from this plan

1) Will there still be enough removal of phosphates and nitrates?

2) How well will the algae react to being turned on and off possibly so much?

3) How quickly would the ph react to the changes in CO2 levels? ( ? how powerful is the scrubber)

4) Many other reasons I still have to realize.

Maybe a two part scrubber system one scrubber to control nutrients and another to control Ph ( the size ratio of the 2 ? )

There might be some fairly obvious problems with this but through experimentation this could be made to work.

Please some input as far as I know this has never been tried. I am far from an expert and only just getting back into the hobby

Thanks for any help.


02-13-2010, 12:21 PM
pH should alway be as high as possible. And a scrubber only increases it 0.1 or 0.2 anyway. So not very useful. What you could is a temp controller, which would turn on/off a fan on the screen.

02-13-2010, 01:55 PM
Thanks for the reply.

"pH should alway be as high as possible" I know next to nothing about SW but there is no way that is true for FW

some exceptions

"And a scrubber only increases it 0.1 or 0.2 anyway" This would be time dependent ( EX. Years ago I put my FW tank way

over 7 because at first I had the scrubber on all the time). As you shift the equilibrium in one direction the ph will go up.

As far as I know. There is also the issue of the buffer capacity which maybe the key

to being able to adjust PH with the method I suggest.

"So not very useful" you might be right but I am willing to try.

"What you could is a temp controller, which would turn on/off a fan on the screen." Good idea.

Thanks for any help.

02-13-2010, 02:11 PM
First, using CO2 to control PH seems pretty dangerous.
I can see pretty wild PH swings if your buffering gets low. Which would likely seriously stress the fish.
Best to just use various types of chemical buffering/alkalinity.

Second, the waterfall effect, with cascading water exposed to atmosphere, probably does far more that the algae.
You would quickly reach normal saturation.
And since you can really only turn the lights on/off, not the pump, or algae will die, not sure how much you can regulate it.

Third, in FW, there is rarely that much CO2 anyway, unless your tank is really sealed, or very heavily populated.
That is why on heavily planted tanks, you have to supplement CO2 constantly.

02-13-2010, 02:40 PM
Thanks for the reply

The algae scrubber is what is adjusting the CO2 levels. amount of buffering is a big ?

Pump never goes off because of these two reactions.

photosynthesis (lights on) takes in CO2 gives off O2

respiration (lights off) takes in O2 gives off CO2

I might not sure that there needs to be great quantity of CO2 to make a lot of difference.

I know from experience that you can adjust ph very quickly by bubbling CO2 through the water.

(water doesn't readily absorb much CO2 from the air because CO2 only makes up 0.038% of the atmosphere)

I might be barking up the wrong tree but I am going by what I have observed through the years.

So please, tell me how it won't work that makes me think of ways that it might.

Thanks for any help.

02-14-2010, 03:10 PM
I see this as being a bit too variable to control in that manner. The absorption capacity will vary, as will atmospheric CO2 concentrations and carbonate alkalinity.

FWIW, CO2 is the major contributor as far as controlling pH in water. The buffering system will resist some change as far as lowering is concerned and it will take a greater quantity of CO2 to make a difference--much more so than in most FW systems. Actually, the bicarbonate/carbonate buffer system is better equipped to handle upward swings more than lower ones, but it does offer some support. Also, respiration in algae and plants occurs 24/7. It's just that the net from respiration and photosynthesis results in an excess of O2.

02-14-2010, 04:26 PM
Thanks for the correction. I would think then an accurate statement might be that when the

lights are off, since photosynthesis is not occurring, there would be a rise in CO2 levels. I should

also be more specific. I want to apply this to a FW discus tank. Ideally a target would be some where

between 6.5-7.5 Some people think that there is no need to keep a discus tank below 7 as once believed.

Fairly consistent ph being more important, this is my motivation to try it. Breeding the exception to this.

Once I get the module that will allow me to get real time ph readings through out the day I will get

a better idea of the normal ph swings in the system. I have not decided how many plants I will have in

the tank, only have one amazon sword now, but I got a fairly stable ph # before by just alternating the

main tank lights and the scrubber lights. So I might be trying something that might not be needed.

In a way I just want to see if it can be done. This in many ways is a work in progress to the point of

possible being a thought experiment to help me understand how the system works.

I did at one time use co2 injection but had no solenoid to turn it off and had to do it manual every night.

I would think this might be something that the controller could turn off at night. Maybe it could keep

some level of CO2 in the system and the ph stable. And also keep some supply of CO2 available for what

ever needs it to keep absorbing nutrients. You could regulate the co2 solenoid with a timer or ph readings.

I am far from an expert so I would welcome anyones corrections or opinions.

Side note I never had a sw tank but I would thing that the controller could be easily made to turn on

and off a FW line to the scrubber to kill pods say once a week.

Thanks for any help

02-15-2010, 10:12 AM
That wouldn't be the difficult part--putting a controller on it, that is. What would be, on the other hand, it accounting for all the changing chemical, biochemical, and biological variables in the process. Just switching the light on to a scrubber when pH lowers seems like a good idea, but it won't be ideal for the scrubber, at least.

02-18-2010, 12:19 PM
Alage does not uptake CO2 and respire in the dark. Just the opposite, just as terrestrial? plants.

See my post on adding CO2. Simply add CO2 to source water not main tank, then off gas prior to return.
High PH water (KH) has so much buffering capacity it will not adversley affect PH. You would just about
have to kill your fish for a drastic PH shift. Try blowing into some sample water and then check PH.

02-18-2010, 02:06 PM
Thanks for the reply.

This is going to be tried on a FW discus tank (possibly below 7 and on the soft water side, small buffering capacity)

Photosynthesis (6) short answer
1)produces food
2)releases oxygen
3)occurs in sunlight
4)stores energy
5)uses water
6)uses carbon dioxide

respiration (6) short answer

1)releases energy
2)uses food
3)produces water
4)produces carbon dioxide
5)uses oxygen
6)occurs in the dark as well as light

I am far from an expert and I might be wrong. I just want to try.

I don't think it could hurt. I will be watching the water parameters.

Thanks for any help.

02-18-2010, 02:37 PM
Alage does not uptake CO2 and respire in the dark. Just the opposite, just as terrestrial? plants.

See my post on adding CO2. Simply add CO2 to source water not main tank, then off gas prior to return.
High PH water (KH) has so much buffering capacity it will not adversley affect PH. You would just about
have to kill your fish for a drastic PH shift. Try blowing into some sample water and then check PH.

They respire 24/7, but only photosynthesize in the dark. Inkidu's summary is correct in how plants work.

Inkidu, if you still want to try, you certainly can. I just don't think it will be as controllable as you'd like and be optimal for your scrubber. Nothing wrong with trying it. Keep us updated.

02-18-2010, 10:26 PM
I did not mean to say they do not respire, I meant they do not perform photosynthesis in the dark, they do respire or breath 24/7, sir you are correct. Thank you for correcting me. :D

Why not just purchase a PH controller with monitor and let it do the monitoring and activating/deactivating
of the solenoid ? Maybe I missed something in your post. :?:

Just info :
I too have a south american biotope, a 70 gallon with about 50 tetras (Hyphessobrycon Columbianus) and Corys. Plants are large and small swords and some duckweed for nitrate removal. With this number of fish they provide all the CO2 the plants require. Water is 2 deg KH and about 4 GH, so it is very soft. I replace evaporated water from a RO unit and then add some carbonates and other essential minerals. It was initially setup in 1993 and has been in operation since. In the past I used CO2, now a timer just turns on a small air pump at night for CO2 reduction. PH is 6.2-6.5. With low PH most nitrogen is ammonium, which plants consume. :mrgreen: