Topping up due to evaporation affects KH?

[Flare]

Hi,

My 50USG has a hardness of 4dKH. I add 1.5 teaspoon of baking soda to raise 2dKH after my 50% water change every weekend. As there is an AC fan running whenever the lights r on, the rate of evaporation is significantly high. I do, however, top up around 1.5 litres of overnight tap water every evening when I return home from work. After topping up, does the KH go down? I understand that in marine tanks, u can safely top up with freshwater because only water gets evaporated, not the salt. Does this theory work for baking soda as well?

Cheers~

[vinz]

When water evaporates, only water escapes. All "impurities" remain in the tank. So, no, your KH will not be affected.

[Flare]

So if the KH goes down, it can only be due to the plants absorbing KH in the form of carbon due to insufficient co2 pumped and high lightings / nutrients. Correct?

[PeterGwee]

I'll look at your substrate first for a start...what kind of substrate are you using at the moment? ADA aquasoil or nisso soil? That will be the cause of it if you are using those substrates. Yes, some plants like vals do use carbonates as a form of carbon if the CO2 is low but not all plants are equip to do it though. Perharps you can give more details on your tank if order to find the root cause of it.

Regards
Peter Gwee

[IUnknown]

All "impurities" remain in the tank

So wouldn't the concentration of bicarbonates go up? If he is adding tap water that would raise the KH.

[bclee]

The good thing is that the tap water here in Singapore have virtually zero KH. (It ranges from <1 to 2 and max 3 sometimes.) So build-up of KH is not an issue when we top up water especially when the water we add is very little compared to the tank volume.

If there is nothing removing KH, theoretically KH should rise every time we top up. In the actual case, like some have mentioned, it might have been some plants consuming the carbonates.

BC

[Flare]

I'll look at your substrate first for a start...what kind of substrate are you using at the moment? ADA aquasoil or nisso soil? That will be the cause of it if you are using those substrates. Yes, some plants like vals do use carbonates as a form of carbon if the CO2 is low but not all plants are equip to do it though. Perharps you can give more details on your tank if order to find the root cause of it.

Thanks Peter. Anyway, My KH is not going down. Everytime, after my 50% water change, I just add Baking Soda to raise it back so my KH always stays at 4dKH. I'm asking to clear my doubts.

The good thing is that the tap water here in Singapore have virtually zero KH. (It ranges from <1 to 2 and max 3 sometimes.) So build-up of KH is not an issue when we top up water especially when the water we add is very little compared to the tank volume.

Yup. I tested our tap water's KH and it turns yellow on the first drop suggesting that the KH is below 1 or even 0.