Will aquarium gravel raise your pH? Yes, And no.

Last Updated on July 15, 2021 by cmoarz

Keeping your aquarium’s pH and water chemical composition balance can be a pretty tricky and delicate process.

Everything you add or do in your aquarium can upset this balance very easily.

That’s why it’s important to know what gravels will raise or power your pH so you can adjust things accordingly, Let’s get started.

Does aquarium gravel raise ph?

Yes, aquarium gravel and substrate can both raise and lower your pH depending on what the material is made out of. For example, limestone gravels will increase the pH, and volcanic rocks will lower pH.

Volcanic Rock

Volcanic rocks, soils/stratums will actually lower your pH level. It promotes a natural to mildly acidic pH. You can raise the ph if need be with a bit of baking soda or some crushed coral shells to counteract the volcanic rock a bit.

Volcanic types of aquarium gravels are good for your aquarium if you have a lot of plants. It’s back with nutrients that plants love to eat. And it will also help you get the water chemistry you want, assuming that’s a bit lower of a pH level.

They are also soft and round (assuming you’ve gotten fluval) and not sharp. So it doesn’t hurt the fish if they dig around in the gravel.

Limestone Aquarium Gravels

These can be a good source of minerals for your fish and plants to live on. However, they will also rapidly raise the ph in your aquarium if used as a substrate or placed under rocks/stones you may have collected from outside.

These stones are made up of calcium carbonate which is basically limestone rock. So it’s best to pick this kind of gravel up at your local pet store to get what you need without having them add unwanted things that could hurt your tank.

Chemical Name for Calcium Carbonate: Calcite (CaCO3)

Wikipedia says: “Approximately 50 percent of sedimentary rocks are limestones.” Does this mean half of all aquarium gravel is limestone? I’m not sure, maybe.

In the aquarium hobby, a lot of aquascapers use it because it’s easy to work with and looks good too. They also add things like aragonite sand or crushed coral gravels to their tank to get a higher ph balance. But if you’re just starting out you may want to stay away from these until you have a bit more experience under your belt so you don’t end up killing your fish off by making the water chemistry too unfavorable for them.

Platic aquarium gravels

Plastic aquarium gravels in your fish tank will have no effect on high ph or low ph and are considered inert. Plastic has nothing related to pH that will leech into the water chemistry aside from whatever dye the plastic may be using.

Even so, I rarely recommend you use plastic for your substrate. Why? Because it leaches chemicals into the water which is easily absorbed by your fish, and that’s never good.

Besides, it’s gaudy and terrible. Go for something more natural. There is nothing more unnatural than SpongeBob decorations and neon pink gravel. Your fish will hate it.


While technically speaking driftwood isn’t a substrate or gravel, it’s certainly an important part of an aquarium if you have one in there so it’s worth talking about as well.

Driftwood will lower pH by little bits. You’ll want to be careful if you have a naturally acidic community tank. It may lower the pH too much to keep some fish happy.

Driftwood also breaks down and releases a bunch of chemicals. Most of them are harmless, but tannins may turn your tank water a bit on the browner side. it’s something to be aware of.

Peat moss

Most people think peat moss is an above-ground only substrate, but actually, it’s often used in aquariums to make part of a nutritious plant root layer.

It retains beneficial bacteria and is known to give nutrients to your plants. But it’s not pH neutral or alkaline in any way, and actually lowers the water chemistry ph level.

Just like driftwood, it will also release little bits of tannins into your tank water so be aware of that.

At the end of the day, remember it’s easier to raise your ph than to lower it. Test the ph levels often, especially when you make changes. There are other factors that go into balancing your ph levels as well, such as dissolved carbon dioxide and dissolved oxygen levels.

Doing plenty of water changes can help lower ph, but a water change will do little good for ph if your tap water already has a high ph. You should test the ph levels of your tap water before or after dechlorinating/treating it.

As for raising ph levels, crushed coral, limestone and cuddle bones, crushed or whole snail shells, etc will do wonders. You can place these things at the bottom of the substrate layer or in the filter itself.

Generally, planted tanks will always have a lower ph level than unplanted tanks, But depending on how much carbon dioxide the plant species puts out, it could also increase it rather than drop it. Counteract this with a bubbler which will break the surface of the water and allow carbon dioxide gases to escape.

Regularly checking your water parameters not just for ph but also for kh (total alkalinity) will tell you what substrate you should or shouldn’t use based on the needs of your water parameters.

Is 8.4 pH too high for an aquarium?

Tropical freshwater fish typically thrive at a pH of 6.8 to 7.6, but certain species require lower conditions for survival. Only you know what’s best for the community species that live in your fish tank.

If 8.4 is too high, consider adding some of the substrates above that are known to lower ph levels.

Will high pH kill fish?

High ph is subjective based on the species you’re keeping. Generally speaking, any ph higher than 9.5 is almost certain death for most fish on planet earth. Very few species can accommodate such high water parameters.

If your water chemistry is approaching these levels and it wasn’t done on purpose, you should treat it as an emergency. Remove what fish are still alive, do full water changes, and try to troubleshoot what went wrong.

Remember fish waste and food waste will increase ph levels. Check the filter to make sure it’s not clogged up with waste which is breaking down into ammonia and ph.

Remove any shells or calcium sources, and investigate the minerals in your gravel as they could be the culprit. Considering using a substrate like volcanic rocks and gravel instead.


Owner of AquariumGravel.com and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!