scrubber effects on alkalinity?

[rwb500]

I searched long and hard and couldn't find a thread dedicated to this:

How badly does an algae scrubber affect alkalinity? I found many mentions that theoretically algae growth can consume bicarbonate, but there are extremely few people complaining about low alk. If I install an algae scrubber, is my ca/alk balance going to be thrown way off? what can i expect? Is it really any better with an upflow design?

thanks!

[RkyRickstr]

After a while when you have really good growth. Garf figured out that if you put bubbles through the screen it reduces this.

I added 1oz of alk per week to compensate.

[SantaMonica]

Welcome.

Most people don't have strong scrubbers so they don't consume any alk. But if you have strong growth quickly, it will pull alk down a few points in a week. A tablespoon or two of baking soda puts it right back up.

Of course even a strong scrubber will slow down if nutrients are brought low in the tank and you don't start feeding more.

[Floyd R Turbo]

Remember that raw baking soda will lower pH, baked baking soda will raise it. IMO the latter is better, or a blend of each. Google it and read up.

[rwb500]

it seems like alk drop isn't a major problem. when algae consume bicarbonate, they release hydroxide. that hydroxide contributes to the carbonate - bicarbonate equilibrium and the net gain or loss of alkalinity is zero. It is a cycle. The algae is not consuming the alkalinity.

[Garf]

Biogenic decalcification

[rwb500]

no, the minor release of hydroxide is not enough to cause any calcium carbonate precipitation in a reef tank. The hydroxide will equilibriate back into the system long before the tank get so out of whack that you get precipitation. plus, that would be a balanced calcium and alkalinity sink. the often-discussed phenomenon is a drop only in alkalinity.

[Floyd R Turbo]

Biogenic decalcification

Google this and read up. If this wasn't the case, then people would not be complaining that their scrubbers are sucking down their alk levels.

[rwb500]

like i said, that is a freshwater phenomenon. a little extra hydroxide is not going to cause anything in a marine environment. plus, decalcification would cause a balanced depletion of Ca and Alk, like I said.

i would love it if someone could propose a chemical mechanism for alkalinity depletion by non-calcifying algae in a marine environment.

[Garf]

like i said, that is a freshwater phenomenon. a little extra hydroxide is not going to cause anything in a marine environment. plus, decalcification would cause a balanced depletion of Ca and Alk, like I said.

i would love it if someone could propose a chemical mechanism for alkalinity depletion by non-calcifying algae in a marine environment.

Have a look at this;
http://algaescrubber.net/forums/showthread.php?2611-Photosynthetically-Induced-Phosphate-Precipitation&p=30279&viewfull=1#post30279

May be because only 20ppm calcium is precipitated, compared to a whopping 2.8dkh alkalinity. Dunno about every else but my calcium test is crap, alkalinity test not so bad. Perhaps the calcium drop just gets missed. In that thread there's a few links that show photosynthetic calcium carbonate precipitation occurs in the ocean. In our tanks, it may well be confused because increasing the pH to 8.4 (a known effect of photosynthesis) also increases precipitation from corals and calcifying algae.

[rwb500]

good thread and good thoughts, thanks. it's true that the Ca depletion could be unnoticed. it's nice to know that even if this is happening, I wouldn't need to mess with my two-part ratios. I just don't see how the local pH on an algae scrubber could ever rise enough to precipitate CaCO3. There's so much more flow than a planted tank. However, I will keep an eye out for it, just like I keep an eye out for any abiotic precipitation in pumps and other places. Many people keep their tanks right on the brink of abiotic precipitation, so maybe in those cases an algae scrubber is all it takes to push it over the edge.

[SantaMonica]

Makes sense that algae would only take the carbon from the alk. The drops in alk therefore could be temporary swings not yet in equilibrium. But I have seen continuous alk drops. Although, each of these drops is with a new batch of algae, so in effect each batch of algae gets one crack at the alk before it is then removed.

[Floyd R Turbo]

But the algae is always growing, now if you clean the screen fully (both sides) then one might expect the rate of alk uptake to decrease until growth picked up, but if someone alternated cleaning sides the excess alk uptake would be more consistent.

I guess there is no hard data on this, just anecdotal reports but they all point to the same result that basically confirms the theory that once algae has taken up the CO2 out of the water, it goes after bicarbonate and your alk drops. I guess I'm not following the whole chemistry discussion about equilibrium and what not.

[tebo]

Well my experience with this is rather long,,, if the aquarium is in equilibrium with respect to chemical and biological load, the ATS has very little impact on the alk,,, otherwise when not in balance

In my experience, when I was the aquarium with a balanced bioload, had to add 5g of baking soda and 5g of baked baking soda a week

When I lost the majority of my fish for ich, leave the unbalanced acuairo This led me talking about the alk to increase a dose of 12gr of baking soda a day, if that dose not add my alk drops dramatically

Throughout this process my ats always grew fairly well and good more so when I could not get a few small fish by not finding

as says floy R turbo,,, when I was fish, plenty of co2 in the water column, but when they died,,, low CO2 and therefore the ATS was after bicarbonate

So, IMHO the ats consume alk depending on the state of balance in the aquarium


regards

[Floyd R Turbo]

Tebo, good point. The more fish / livestock, the more natural respiration is happening, the more CO2 is being produced. So the answer to the dropping alk is....ADD MORE FISH!!

[Garf]

Tebo, good point. The more fish / livestock, the more natural respiration is happening, the more CO2 is being produced. So the answer to the dropping alk is....ADD MORE FISH!!

or aerate, or increase scrubber flow, or all of these.

[rwb500]

none of this is very compelling. I'm going to assume that it's impossible for non-calcifying algae to significantly affect Ca and Alk levels. I encourage you all to take another look at this theory, and see if any of your future alk swings can be blamed on something else.

[Floyd R Turbo]

As with many things in this hobby, we are forced to rely on anecdotal evidence to confirm a theory. In this case, this has been confirmed by many, many people as indeed true. Personally, when I was running a large scrubber (oversized) it was sucking alk down like crazy. When I switched to the feeding-based sized scrubber, alk uptake levelled off a little more. It still get taken up faster than CA, but they are mush more in line.

[kerry]

I can dose 2-4 quarts of saturated (with vinegar) lime water (Home made Kalkwasser) into my 40G breeder every day since my scrubber was changed over to LEDs when we all started testing them with the addition of a blue LED. I can say that the LED set-up increased my algae growth a ton as did my ALK consumption. On the other hand my CA is not taken up near as fast as Floyd states so I sometimes only does Baking Soda because I dont need the CA once it hits 600+PPM. So basically I can drop 2-4 points in ALK in a day once I near my two-ish week cleaning. This rate of drop is related to growth of the algae. At the top of the screen cleaning I might only dose a quart of KALK every day or every other but once into it about 3-4 days its at least a quart then by a weeks time its about 2 quarts a day and only gets heavier into the algae growth cycle.

[Nick28]

I think maybe high ph levels on the screen may cause precipitation into calcium carbonate? That combined with small but numerous calcifying animals on the screen? I don't think the algae itself keeps any alk maybe a little calcium.

[kerry]

I think maybe high ph levels on the screen may cause precipitation into calcium carbonate? That combined with small but numerous calcifying animals on the screen? I don't think the algae itself keeps any alk maybe a little calcium.
Why do you say algae does not use (keeps) any ALK? What would it consume if it does not use (keep) a carbon source. Maybe I am not fallowing what you mean????

[Nick28]

Why do you say algae does not use (keeps) any ALK? What would it consume if it does not use (keep) a carbon source. Maybe I am not fallowing what you mean????

I believe the mechanism is carbonic anyhydrase algae grabs bicarbonate removes carbon releases hydroxide and it reforms at the surface. Corals inbed HCO3 in their skeleton causing depletion

[kerry]

Ok, so we are the same thinking. In the end the ALK (carbon) is used by algae. I am never low on CA seeing I dose saturated Kalk.

[Nick28]

Ok, so we are the same thinking. In the end the ALK (carbon) is used by algae. I am never low on CA seeing I dose saturated Kalk.

yes but its returned 100%, I'm trying to find out were the loss is coming from that people complain about im guessing its calcyfing animals on and under the screen those little white shell animals that stick to everything that are removed during cleaning and high ph on and around the screen causing precipitation.

I can't remember who did it but I want to say GARF, found the precipitation of phosphate on the surface of algae, calcium carbonate may also precipitate taking some bicarb with it. At least its precipitating phosphate.

[kerry]

If its (the returned carbon) anything like DOC then the bacteria will consume it and so will coral.

[Nick28]

If its (the returned carbon) anything like DOC then the bacteria will consume it and so will coral.

yes, but I'm talking about the hydroxide (OH) release going to the surface and rebinding with the airs CO2 to form new Bicarbonate (HCO3) keeping equilibrium with free hydroxide and CO2.

basically how kalk works. (As long as you don't overdose or add too much too soon)

The precipitation on the algae may create an aragonite like compound if the PH is driven high enough by photosynthesis on its surface.

[kerry]

I even have two fans blowing on my water fall scrubber and I cannot really say I see any type of equilibrium as I hoped to when this method was first discussed a couple years ago or so. In theory I really thought I was onto something when I started this dosing Kalk and newly added fan with my scrubber thing but I was wrong. I have however saved a TON of cash using this method of homemade Kalk. I am not sure the OH makes it past the bacteria in my tank (40G breeder open top). I know what you are saying but I dont see this happen at all, even in my covered 150G. I kinda gave up on all the high tech reads on this stuff and just stick to doing this method because it works for me because what is suppose to happen does not in my tanks. So I have chalked it up to the bacteria consuming this left over material. I am not sure how long the OH can stay in its current form all the way to the surface anyway, surely something else reacts with it or something like bacteria consumes it.
Also be sure not to mix up basicity with alkalinity.

[SantaMonica]

I have seen the holes in the waterfall screen filled in with a lime type material sometimes.

[Nick28]

I have heard of alkalinity loss in scrubberless, refugiumless tanks as well. Corals do take up more alk than calcium

calcium carbonate is about 60/40 by weight bicarb (3 oxygen, 1 carbon)to calcium(1 calcium).

If you search some of the web forums people seem to complain about alk dropping faster (common problem).