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Established Scrubber & Alkalinity levels

Discussion in 'General Discussion' started by TbyZ, Jan 5, 2017.

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  1. TbyZ

    TbyZ Member

    Hi All;

    From what I have read, one Reef tank rule or thumb is:-
    High nitrate, maintain high alkalinity.
    Low nitrate, maintain low alkalinity.

    What I have noticed with my tank, since nitrate & phosphate became undetectable using test kits, is that my alkalinity is always low, at around NSW levels. Even after raising it, it drops back down after a few days.

    This isn't necessarily a problem as I would be aiming for a low alkalinity level, and the pH is fine. But I am curious if anyone else has experienced this same reaction, & what may be the reason?
    Especially if anyone has had the situation where alkalinity fell too low and it became a problem maintaining it at a reasonable level.

    I'm guessing that carbonates are stripped from the water and utilised for the production of algae for the same reasons CO2 is necessary. This is why alkalinity remains low.

    The tank is 50 gal. Live rock, corals, fish - scrubber 4 cube (feed two cubes) - activated carbon and filter sponge 50% of the time only. Water change - 25% NSW every 1 to 2 months. RODI top up.
  2. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    Can't say I've heard this before, but then again I haven't researched much lately.

    I had always heard that if you are running a FOWLR, you can keep alk high, like 12. But for a reef, 9 to 11 is preferred. Then I have heard that if you are running ULN like Zeovit, you want to get it to 7.0 before you even start dosing Zeovit, and have had a couple local reefers tell me that keeping alk at 9 or lower is preferred...
  3. TbyZ

    TbyZ Member

    Hi Turbo;

    Quote from - Optimal Parameters for a Coral Reef Aquarium: By Randy Holmes-Farley

    Many aquarists growing SPS corals and using Ultra Low Nutrient Systems (ULNS) have found that the corals suffer from burnt tips if the alkalinity is too high or changes too much. It is not at all clear why this is the case, but such aquaria are better served by alkalinity in the 7-8 dKH range.

    Optimal Parameters for a Coral Reef Aquarium: By Randy Holmes-Farley
    Turbo likes this.
  4. TbyZ

    TbyZ Member

    found an interesting article on this exact topic.

    Photosynthesis and the Reef Aquarium,
    Part I: Carbon Sources


    This graph, showing concentrations of carbonate, bicarbonate & CO2 in seawater at various pH concentrations, explains why algae uses bicarbonate for photosynthesis. Note the fraction of CO2 at a pH of 8.

    Turbo likes this.
  5. TbyZ

    TbyZ Member

    What I have learned, & following on from the above graph;

    seawater at a pH of 8.2 has almost no CO2, or carbonic acid.
    The carbonic acid that is formed, when carbon dioxide hydrates, very quickly equilibrate into the water's carbonate buffer system, converting into both bicarbonate and carbonate by releasing protons (H+). The primary factor that determines the relative amount of each species at equilibrium in seawater is the pH, with a small temperature effect as well.

    Bicarbonate is then the predominant source of CO2 for seawater photosynthesising organisms.

    Many marine algae and other organisms take up some measurable portion of the carbon dioxide that they incorporate during photosynthesis. But, in most cases this process can account for only a portion of the demand for carbon dioxide.

    The rate at which carbon dioxide is used by rapidly photosynthesizing organisms is fast enough that organisms can deplete the carbon dioxide in the surrounding seawater faster than it can be replaced by diffusion and other transport mechanisms through the seawater.

    So, if the incoming CO2 is rapidly being used up before it is hydrated into carbonic acid, & then consequently bicarbonates, the alkalinity falls (but stabilizes at 125ppm in my case).

  6. atoll

    atoll Member

    My params using a DIY waterfall ATS.
    NO3 = 5ppm
    PO3 = 0.03ppm
    KDH = 5.6 Yes low.

    Everything looks good.
  7. TbyZ

    TbyZ Member

    KDH = 5.6

    do you try to raise it at all?
  8. atoll

    atoll Member

    I used to but stopped chasing numbers as it would always fall back to around 5.6 kdh
  9. TbyZ

    TbyZ Member

    did you use bicarb or kalkwasser?
  10. atoll

    atoll Member

    kalkwasser connected to an ATU.
  11. TbyZ

    TbyZ Member

    That could be the problem.

    from Photosynthesis and the Reef Aquarium, Part I: Carbon Sources

    "Do not drip limewater (kalkwasser) into or upstream of a lit macroalgae refugium (or scrubber), because it limits availability of CO2."

    limewater consumes carbon dioxide in the water so it never gets to convert into bicarbonates & carbonates.

    Try topping up with bicarb instead. You should be able to keep the alkalinity at around 130ppm, or 7.2dKH in your measurement.
  12. atoll

    atoll Member

    Cheers, All looks well however and I have heard similar stories of tanks running low KDH but doing just fine. What I would like is 2 ATU reservoirs one feeding my Kalk stirrer at night and bicarb during the day with a solenoid on a simple plug in timer switching the reservoirs over but so far I haven't been able to find anything suitable.
  13. TbyZ

    TbyZ Member

    Maybe a calcium reactor might be easier
    atoll likes this.
  14. atoll

    atoll Member

    I have one of those as well but took it offline as my calc was going too high with the Kalk stirrer as well. I could drip kalk before my ATS if that would make a difference?
  15. TbyZ

    TbyZ Member

    apparently its best not to use Kalk at all if your growing algae.
  16. atoll

    atoll Member

    Hmmm not heard that before.
  17. Turbo

    Turbo Does not really look like Johnny Carson Staff Member Site Owner Multiple Units! Customer

    Can't say I've heard that either but the explanation makes sense. Might answer a few questions / solve a few problems too.

    I'm sure there is a caveat to that. Some people with heavy SPS tanks will drip kalk because they can't dose 2-part enough due to maximum/day amounts, also it's not ionically balanced. But the larger the tank, probably the lesser effect it has on algae.

    When troubleshooting I have never really asked "do you drip kalk" maybe I will now....
  18. trivodi

    trivodi Member

    If CO2 is the problem you can run an air stone24/7, thats what I do since i dont have a skimmer and I ran algae scrubber only. I dont have an issue with my alkalinity and my nitrate is 0.2-0.5 and phosphate 0.01-0.03
  19. TbyZ

    TbyZ Member

    I learnt some time ago that my assumption here in this thread, that alkalinity levels fall as a result of algae photosynthesis, was incorrect.
    Algae can & does take up CO2 for photosynthesis directly from bicarbonates. But the remaining hydroxides soon take up C & O to form bicarbonate once again.
    Just like with kalkwasser (calcium hydroxide) its the hydroxide that raises alkalinity by forming bicarbonates.

    My alkalinity was falling, but via some other mechanism. Probably the incredible increase in coralline algae growth that took off after my PO4 levels fell from a rather high content.

    Thanks Randy.

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