The Effect Of Limestone On A Freshwater Tank

We know as hobbyists that our water parameters can change. Water can have slow and steady changes in PH for instance. And fast wild swings.

PH is a measure of acidity versus alkaline with a score of seven being neutral. Anything lower than seven is considered more acidic anything above seven is considered more alkaline.

So I’m writing this post to clarify the effect of limestone on a freshwater tank as well as the effect limestone has on freshwater tanks.

With that being said let’s have a look at limestone in our fish tanks. First a quick brief and then a deeper more in-depth look.

We will be looking at the water hardness or GH General hardness. PH Potential hydrogen and of course KH Carbonate hardness. As these parameters are important but often misunderstood.

What Effect does limestone have on a freshwater tank?

Limestone gives nutrients to both fish and plants mainly calcium helping them grow and also keeping the water clean by removing and filtering iron salts and algae from the water.

Does Limestone Raise The Ph Level?

Well, there may be a slight change in ph as limestone over time takes acidity out of the water. This would happen anyway.

There are a plethora of things that happen in a tank that changes the ph on a daily basis. Fish poop changes ph the food they eat changes the ph. 

If at all interested in Fish poop and how important it is for our tanks. Check out Do fish poop and How fish poop not to mention Why fish poop. If you have time there’s always What is fish poop

Plants will have major swings in the ph of a tank. During the day they are in photosynthesis. Breathing in carbon dioxide and expelling oxygen.

At night it’s reversed and they breathe in oxygen and expel carbon dioxide. These are just a couple of things we as hobbyists deal with daily.

What Is The PH Of Limestone?

What I’m trying to say and emphasise is PH levels fluctuate daily because of a multitude of things and it’s not as important as people make out.

As PH only tells us how acidic or alkaline our water is. With that being said what is the PH level of limestone .

Oh boy, check the article above but yep you probably guessed it’s seven (7) that’s right seven ie PH neutral.

Also in testing limestone is effectively insoluble in pure water. Most of us are trying to use pure water id assume.

So What PH Do Fish Need?

Freshwater fish will do fine anywhere between PH Six (6) & Nine (9) that’s a fairly big gap. Obviously, I wouldn’t expect fish tanks to fluctuate this much daily.

That being said you can expect a swing of one (1) whole point on a day-to-day basis.  Please remember we are speaking about PH this has nothing to do with hardness as people seem to think.

PH only tells us how much potential hydrogen there is. So what about KH carbonate hardness maybe this will be problematic for limestone in a freshwater environment.

KH Carbonate Hardness & Limestone

Most hobbyists like to have a buffering effect when it comes to KH. In essence, we are trying to

gently raise the KH level. When describing this to people it’s probably best described as a large bin.

The more KH the bigger the bin. This is because a bigger bin will keep the rubbish in. Overfilling the bin would result in a PH crash.

KH is essential for all fish and plants if the KH was zero (0) the tank would simply crash. The general rule of thumb is around eight (8) for freshwater fish.  Or around 140 parts per million.

What about limestone though? I hear you jeez I have to explain all that to say limestone will raise KH but that’s not necessarily a bad thing.

And it will raise slowly as it’s not very soluble in water as said before. Also the plants and fish are going to take the calcium out first and that’s beneficial.

KH And Water Hardness

KH or carbonate hardness measures the specific amount of carbonates and bicarbonates that are in the water.

KH is not a measure of water hardness this would be GH or general hardness we will get to that in a bit stay tuned.

We need this carbonate hardness in order to protect our tanks. Carbonates are two forms of compounds carbonic acid and carbon dioxide.

Acids are salts and carbonic acid and are considered inorganic. Carbon dioxide is in the form of a carbonate ion or metals such as sodium and calcium.

Bicarbonates are one (1) carbon atom surrounded by three (3) oxygen atoms. How this looks in a freshwater tank here is an example.

How KH And PH Work Together

One example would be in a planted tank. Photosynthesis happens in the daytime with the release of oxygen into the water and at the same time releases bicarbonate ions.

This process raises PH while at night plants go into respiration processes and release carbon dioxide but no more bicarbonate ions.

Resulting in a sharp drop in PH levels. Adding some limestone will help control these shifts as well as help over time to raise KH.

Which in turn acts as a buffer barrier to protect your tank from sudden crashes.

GH General Hardness Of Water

General hardness is the test that would determine the hardness of your water, not the KH test. GH tests or measures for minerals specifically calcium and magnesium.

We as hobbyists test our water to see how hard or soft it is in order to check for minerals that are essential for the health of the tank.

As we need certain amounts of calcium magnesium as well as salts for the development of fish shrimp snails and plant life.

Did you know there are a few snails and other sea life with shells made of limestone check this little dude out he has eyes made from limestone What are Chitons?

Again limestone will give the tank enough calcium and won’t overdo either the PH as limestone has a neutral seven (7) and on its own will not chemically on its own raise above eight (8).

Again KH limestone will barely raise over time by one (1) let’s be generous and say two (2) degrees.

As said earlier this is not a problem as we should gently raise KH to help protect against crashes in PH think about making a bigger bin and stopping problems from overflowing.

What About Limestone On GH Water Hardness

Limestone will as we’ve been saying raise all parameters slightly but there’s an equilibrium point where everything levels off.

This is true for hardness too. We have very hard water where we live and I’m sure there are plenty of other places with similar hardness.

We currently have around 200 million parts around a GDH of twelve (12) Freshwater fish need around 140 million parts around eight (8) GDH.

Personally, I believe fish need more as we’re in an average GH so I think fish can easily adjust to their surroundings. 

Twelve (12) has never caused us any problems and this is because most people’s water has limescale from limestone in the water as it’s got a healthy amount of calcium.

What About The Benefits Of Limestone

Ok, this is where things get interesting as there seem to be some really good benefits. We are hopefully gonna see the overall effect limestone can have on a freshwater tank.

So hopefully you’re still with me while reading. I know it can be hard dealing with the science PH levels KH and GH and then DGH the list goes on.

We need to know these details as they can help keep our tank healthy. Plus people pay too much attention to one part or another and not the whole package.

Back to the advantages of limestone in our tanks. First, they help slowly raise the KH and this, in turn, stops PH crashes.

The second thing is limestone leaches those minerals mainly calcium that fish and plant life need to keep them healthy. Fish for bones and growth and plants for growth.

Thirdly they take excess dioxide out of the water which is awesome for fish and helps reduce the overall bioload.

Fourthly limestone will absorb iron and salt and remove them from the water.

Five on the list is filtering the water and keeping it clearer for our viewing pleasure. 

Believe it or not, this amazing rock limestone can even keep algae under control. Limestone removes phosphates from the water.

Stopping algae from growing.

In Conclusion Limestone & Its Effect On A Freshwater Tank

In conclusion, limestone has an overall positive effect on our freshwater tanks. It will slowly raise PH but ph is not anything to be overly concerned with.

Unless it’s too low And the same can be said for KH. which needs to be slowly raised in most cases as it’s much more manageable to have higher KH.

As this will stop crashes in the tank and give you more time to control any changes in parameters. Hard water GH will rise slightly but not by much as limestone is not very water-soluble.

The benefits are amazing giving nutrients and calcium to both fish and plants allowing for bone health growth of both fish and plants.

As well as taking and removing phosphates from the water. Which keeps algae under control.  Taking irons out and excess salts filtering the water keeping it crystal clear.