Why does Alkalinty drop in an empty tank?

[Joe Batt]

Why does my alkalinity slowly drop in a tank with no corals? (approx 0.4dkh every 4 days) Ca Mg is constant at the moment.

I have restarted my tank and through the cycle is finished I currently have an algae bloom.

The tank just has 7 medium sized fish, cycled rock and sand (originally dead dry rock), a refugium with a refugium some cheato and is running a skimmer ROWA and carbon.

 

[Crabs McJones]

Why does my alkalinity slowly drop in a tank with no corals? (approx 0.4dkh every 4 days) Ca Mg is constant at the moment.

I have restarted my tank and through the cycle is finished I currently have an algae bloom.

The tank just has 7 medium sized fish, cycled rock and sand (originally dead dry rock), a refugium with a refugium some cheato and is running a skimmer ROWA and carbon.

How much coraline algae do you have?

 

[Joe Batt]

At the moment....none. The tank has only just cycled. Doesn't Coraline drop Ca though not Kh?

 

[rockskimmerflow]

Why does my alkalinity slowly drop in a tank with no corals? (approx 0.4dkh every 4 days) Ca Mg is constant at the moment.

I have restarted my tank and through the cycle is finished I currently have an algae bloom.

The tank just has 7 medium sized fish, cycled rock and sand (originally dead dry rock), a refugium with a refugium some cheato and is running a skimmer ROWA and carbon.

I'm sure Randy can give you all the scientific detail, so I'll just offer in simple terms that the nitrogen cycle processing organic waste in our aquariums will cause alkalinity to drop as an inherent byproduct of its operation. If I remember correctly, bacterial denitrification will restore the alkalinity removed from solution by the the primary nitrogen cycle, but direct nitrate uptake by chaeto or other organisms will not.

Alkalinity drop is normal and expected in a tank with 7 medium sized fish. Buffering your alkalinity with a simple diy formula should be sufficient if no corals or significant coralline algae are calcifying in the system.

 

[Randy Holmes-Farley Verified Community Expert]

Yes, if nitrate is rising, the production of that nitrate consumes alkalinity. 50 ppm nitrate produced reduces alkalinity by 2.3 dKH.

Also, every tank has some abiotic precipitation of calcium carbonate. Deposits on heaters and pumps, if not elsewhere on rock and sand. And before you say that isn't it because calcium is not declining, you always detect the alk drop long before you are able to distinguish the calcium drop with a kit. A 1 dKH alk drop (easily detected) only corresponds to about 7 ppm calcium drop, which is not reliably detected by most kits.

 

[Joe Batt]

Thanks Randy, I realise that Ca doesn't show the drop like Kh. Interesting to read the reasoning behind the Kh drop, learn something everyday......now I just need the bloom to clear and I will be away ....again....

Currently buffering the Kh with a few grams of Sodium Bicarbonate every few days. Not critical at the moment since no corals.

Nitrate is around 7ppm and Po4 0.08 and slowly reducing

 

[Randy Holmes-Farley Verified Community Expert]

Thanks Randy, I realise that Ca doesn't show the drop like Kh. Interesting to read the reasoning behind the Kh drop, learn something everyday......now I just need the bloom to clear and I will be away ....again....

Currently buffering the Kh with a few grams of Sodium Bicarbonate every few days. Not critical at the moment since no corals.

Nitrate is around 7ppm and Po4 0.08 and slowly reducing

That's sounds like a fine plan.