A Weird Advice From Lfs Guy

[AquaPit]

Hi

I was at a lfs this afternoon..

I asked questions about some ph readings and water hardness..

And the lfs guy gave a weird advice..

Is it true that if you dont clean your filter media at least once a week, the ph will rise??

Pls clarify.. haha

 

[TwoTankAmin]

Nope not a word of truth in that.
 
However, the nature of the cycle is that it will eventually cause the pH to drop if one does not do water changes or have a lot of plants. That is because nitrate produces some nitric acid which will lower pH. It takes some time because of the KH in ones tank. However, regular water changes (or plants) remove nitrate and prevent any real drops in the pH. This is the cause of the pH drops typical with old tank syndrome.

 

[StevenF]

If you don't replace some of the old water with clean water or replace the charcoal in the filter periodically the water chemistry will start to change.  Ammonia is a base, nitrate is a acid.   A buildup of these gases could cause the PH to change.  however the toxic nature of these gases will affect the fish long before you see significant change in PH.  CO2 is also an acid.  So an increase in CO2 can also lower  PH. The total Alkalinity of the water will also work to prevent significant changes in PH.  
 
However in a planted Aquarium plants will extract Calcium and magnesium from the water.  That reduces the total alkalinity and when that drops the PH will  also likely  drop.  Also as calcium and magnesium levels drop plant growth in the aquarium will slow and as a result they may remove less nitrogen from the water allowing nitrite to increase causing additional drop in PH
 
How much of a PH change that will occur is dependent on a lot of  things in the aquarium.   As a result it is not predictable.

 

[TwoTankAmin]

Steven-I think you meant to type nitrate not nitrite when talking about planted tanks.
 
Also, considering that:

In freshwater aquariums, most of water's buffering capacity is due to carbonates and bicarbonates. Thus, the terms ``carbonate hardness'' (KH), ``alkalinity'' and ``buffering capacity'' are used interchangeably. Although technically not the same things, they are equivalent in practice in the context of fishkeeping.

 
The bacteria involved with the nitrogen cycle in tanks need inorganic carbon. They get this from the carbonates and bicarbonates associated with KH. So, even without the effects of nitric acid from nitrate, there will be a depeletion of KH by the bacteria over time. This will also contribute to the potential for a pH drop as well as the acid. This is also why any good fishless cycling article should advise folks to monitor their KH. When the bacteria extract carbon and lower the KH, this can facilitate a drop in pH in addition to the acids involved. This is also why one is advised, during a fishless cycle, to add sodium bicarbonate (baking soda) to a tank.
 
In terms of calcium and magnesium,
 

General Hardness (GH)
 
General hardness (GH) refers to the dissolved concentration of magnesium and calcium ions. When fish are said to prefer ``soft'' or ``hard'' water, it is GH (not KH) that is being referred to.
 
Note: GH, KH and pH form the Bermuda's Triangle of water chemistry. Although the three properties are distinct, they all interact with each other to varying degrees, making it difficult to adjust one without impacting the other. That is one reason why beginning aquarists are advised NOT to tamper with these parameters unless absolutely necessary. As an example, ``hard'' water frequently often comes from limestone aquifers. Limestone contains calcium carbonate, which when dissolved in water increases both the GH (from calcium) and KH (from carbonate) components. Increasing the KH component also usually increases pH as well. Conceptually, the KH acts as a ``sponge'' absorbing the acid present in the water, raising the water's pH.
 
Water hardness follows the following guidelines. The unit dH means ``degree hardness'', while ppm means ``parts per million'', which is roughly equivalent to mg/L in water. 1 unit dH equals 17.8 ppm CaCO3. Most test kits give the hardness in units of CaCO3; this means the hardness is equivalent to that much CaCO3 in water but does not mean it actually came from CaCO3.

 
Calcium carbonate will raise both GH and KH. The calcium will raise the GH while the carbonate raises the KH
 

To raise both GH and KH simultaneously, add calcium carbonate (CaCO3). 1/2 teaspoon per 100 liters of water will increase both the KH and GH by about 1-2 dH. Alternatively, add some sea shells, coral, limestone, marble chips, etc. to your filter.
 
To raise the KH without raising the GH, add sodium bicarbonate (NaHCO3), commonly known as baking soda. 1/2 teaspoon per 100 Liters raises the KH by about 1 dH. Sodium bicarbonate drives the pH towards an equilibrium value of 8.2.
 

 
All quotes from http/fins.actwin.com/mirror/begin-chem.html