BioPellets and Bacteria increasing Alk consumption?

[re76]

So I have started noticing a trend recently.

For some background I have a Reefer 450. I use an avast Kalk Reactor to provide my top off. I am running GFO + Carbon in a reactor as well as biopellets in another reactor.

I had been running the biopellets in an Avast Marine Spyglass reactor since my tank was cycled, little did I know though the effluent flow into the reactor (it is recirculating) was pretty much non-existent.

I noticed this about the same time I started using the Aquaforest system. With Aquaforest I am dosing 2 drops of their bacteria on a daily basis along with increasing the effluent flow into the biopellet reactor.

Up until I started the bio-pellets and bacteria my alk and Ca were solidly maintained by just the Kalk. Interesting enough though I have started to notice about a .5 dkh drop in alk per day.

I test alk every day at roughly the same time in the morning. I have been dosing Sodium Carbonate to maintain my Alk at 8 dkh since I noticed it start dropping.

Can anyone think of any reason this might be happening?

I should also mention I have a very lightly stocked tank. A few small frags of birdsnest, a couple pieces of red monti cap, one piece of a purple monti cap, a medium size wall type hammer, a few assorted acro frags, and a small to medium frogspawn, about 7-8 heads.

My theories are:

• Aquaforest is making my corals grow faster and thus consuming more alk (and Ca)?
  • This doesn't make sense to me though because I have yet to see Ca drop. It has only been a few days, and I know Alk drops much faster than Ca so I am not writing this one off yet.
• I had something die in my tank (haven't seen my nassarius snails in a while), which has caused excess acids in the tank.
  • The acid production as part of the decomposition is dropping my alk and the biopellets and bacteria are quickly removing the resultant nitrates.
• The effluent flow through the biopellet reactor is still too low and the bacteria are somehow deriving carbon from the carbonate in the water.
  • I don't even know if this makes sense chemically....

 

[Randy Holmes-Farley]

When alk and calcium demand increase, you see it first in alk.

Bacteria consuming biopellets do not consume alk. It is even possible they generate it if nitrate is declining (alk rises from declining nitrate, drops from accumulating nitrate).

 

[re76]

Thanks for the quick response Randy. I will continue monitoring and see if I notice the Ca start dropping as well.

I am just sort of confused because I don't feel like my tank is even well stocked enough to be needing saturated Kalk for top off. When I first started using Kalk for all my top-off I expected to have to reduce excess Ca and Alk through water changes. That was worth it for me for the PH benefits though. To my surprise I noticed that everything was quite stable.

My tank is rimless as well so the evaporation is pretty significant.

As a side not I want to thank you for all of the great articles you have written and all you have done for the hobby! I have thoroughly enjoyed reading and learning from your work.

 

[Randy Holmes-Farley]

Running GFO can increase alk and calcium consumption for multiple reasons, including increased calcification by corals as phosphate drops, and increased abiotic precipitation of calcium carbonate on the GFO induced by the iron, and possibly elsewhere as well due to iron being elevated and phosphate being lower.

 

[Randy Holmes-Farley]

Thanks. :)

 

[skim]

I can not remember where I seen some tests on GFO and Alk but in every test Alk would drop to the 7.5 to 7 dkH mark. If Alk was high like 12 it would drop very quickly and slow as it got closer to the 7 mark and if was on the lower side 8 - 9 it would drop more slowly to 7 -7.5. i found it interesting on the fact it would take it the 7 mark consistently but not below it would stay a that level. It goes to show that how you could effect your Corals by going from 12 to 7 in a day. My question is does this leave the GFO useless for Phosphate removal after removing all that Alk?

 

[Randy Holmes-Farley]

I can not remember where I seen some tests on GFO and Alk but in every test Alk would drop to the 7.5 to 7 dkH mark. If Alk was high like 12 it would drop very quickly and slow as it got closer to the 7 mark and if was on the lower side 8 - 9 it would drop more slowly to 7 -7.5. i found it interesting on the fact it would take it the 7 mark consistently but not below it would stay a that level. It goes to show that how you could effect your Corals by going from 12 to 7 in a day. My question is does this leave the GFO useless for Phosphate removal after removing all that Alk?

GFO accelerates the precipitation of calcium carbonate for a variety of reasons, but usually does not make a tank rapidly drop from 12 to 7 dKH. If the GFO gets coated in calcium carbonate it will become less effective, yes.

 

[re76]

I removed the GFO this morning. We can see what effect that has.

My usual routine is to measure Alk in the morning and depending on what it is, dose enough sodium carbonate to get things back to 8 dKH. This usually ends up being about a 1/2 tsp of sodium carbonate for my tank, or about .45 to .5 dKH. I have been doing this now for about a week.

Yesterday I tried an experiment. When I got home in the evening I tried dosing an additional dose of Sodium Carbonate. The same dose that I do in the morning. My thought was that by doing a double dose when I measured the next morning (today) I SHOULD be at 8 dKH since the morning dose would take care of the normal consumption, and the additional dose would carry me into the next day at 8 dKH instead of 7.5 dKH.

That was not the case. This morning when I measured Alk I was STILL at 7.5 dKH. What gives? Could the additional dose have boosted the PH which in turn increased the Alk consumption such that I was still at 7.5? Should I continue increasing the dose until I measure in the morning and it is at 8 dKH?

Depending on what happens with the GFO offline now I might have to start thinking about two part dosing. Is there any reason not to run Kalk AND two part? I really like the Kalk for maintaining my PH.

 

[Randy Holmes-Farley]

The consumption of alk and calcium increases as you increase the alkalinity, and drops as it lowers. That negative feedback loop helps keep alk from rising or falling as much as one might expect from dosing changes.