What's causing low ph (5.0)?

[tropical-fish]

Hey there!

I’m having a problem identifying what is causing the ph of my tank to be so low at 5.0 (and that’s the lowest my test kit reads).

Here’s the setup:
Substrate and decor: Dennerle Crystal Quarz Gravel-Diamond black (ph neutral according to the manufacturers website) and some river rocks.

(A sample of the gravel and all the rocks have been removed and tested by soaking in buckets of water for 8 hours now and ph is still 7.0. I'll keep them soaking for a few days to see if anything changes).

My filter is an FX5. Top tray is filter wool and Seachem Purigen, 2nd tray Seachem Matrix, bottom tray JBL Micromec sintered glass balls.

The only chemical I add to the water is Seachem Prime.

Tank size 48L x 24H x 18W
Ammo: 0
Nitrite: 0
Nitrate: around 10 – 20
Water changes of at least 30% per week.
My tap water ph is 7.5 straight from the tap and 7.0 by the next day.

Ideally I'd like the tank water at ph7.0 to match the tap water without adding any chemicals.

Thanks in advance for our input.

 

[Jonnypro]

I'm going to follow. My ph has been low too what do you have as far as stocking in your tank?

 

[tropical-fish]

what do you have as far as stocking in your tank?

Stock is 1 small rtg arowana and 1 clown loach.

 

[Rivercats]

It's hard to say what is causing your ph to drop so low but I'd be curious to know what your tap waters Kh and Gh are. But what you can do is get some crushed coral and either place it in your filter or in a media bag hung under your filter outflow. CC will add natural buffers back into the tank raising your Kh which will in turn raise Ph. You could start with a cup of CC and monitor the tank for several days and see if Kh and Ph has increased. Then you may have to either add or remove CC until you find the right amount to keep your levels where you want. Also several types of rocks contain calcium which can also be used in a tank to add buffers. The only problem with this method is that it's harder to get the right amount in the tank.

 

[Fishfur]

If possible, get a GH and KH test kit, or get the local store to test it for you, if they will do those tests. pH can become unstable if the water has little buffering capacity, which is to say, minerals in it such as calcium. Should tell you something useful.

KH is a measure of carbonate hardness, calcium levels. GH is general hardness, or all the mineral content taken together. There is relationship between hardness and pH, and it's complex, to say the least. I'm still struggling to understand it all clearly, but I keep learning. Wish I'd paid more attention back in high school chemistry though.

It won't be the rocks causing the acidity. More commonly it is organic stuff that will acidify water, things like peat moss or leaf litter. Usually rock will harden water, as minerals dissolve into the water from the rock. Acid water actually dissolves a lot more minerals from rock than alkaline water can.

 

[Rivercats]

As I already stated many rocks can add buffers into the water and a good way to find out if a rock has this capability is to drop a few drops of vinegar onto a rock. If it fizzes or bubbles then the rock contains calcium and can be used as a way to increase Kh/buffers into your tank.

Just do this test on your river rocks which will tell you if they have calcium which I'm pretty sure they won't.

 

[Fishfur]

I prefer to use a stronger acid on rocks to test for calcium. CLR is a good one, and easily rinses off. You will get reactions with it much faster and it will react to much lower concentrations of calcium than ordinary vinegar will. Does cost more, I grant you. But if you have concerns about a rock leaching calcium, say, into your shrimp tank, it will give you better information than vinegar will.

 

[Rivercats]

Vinegar may not be as precise but its safer to use by far and safe in small amounts if it gets into ones aquarium. CLR can be dangerous if not handled properly and gloves should be worn. There is also the potential problem of it not being able to be rinsed clean off porous rocks, which most calcium leaching rocks are. Extreme caution should be used when using any type of cleaner on objects that are to be placed in aquariums. If a person is knowledgeable and comfortable working with stronger chemicals that is fine but personally it's not something I would recommend for most people.

 

[Fishfur]

I am quite obsessive about rinsing and washing off anything I use, so I have no problems with it.

But shame on me for not making it clear it needs to be thoroughly rinsed off.

 

[foster53]

I prefer to use a stronger acid on rocks to test for calcium. CLR is a good one, and easily rinses off. You will get reactions with it much faster and it will react to much lower concentrations of calcium than ordinary vinegar will. Does cost more, I grant you. But if you have concerns about a rock leaching calcium, say, into your shrimp tank, it will give you better information than vinegar will.

Why would you recommend using a strong acid cleaner to test the rocks. In porous rock there is a chance it will not be rinsed completely out of the rock. Vinegar is much safer, and if its not all rinsed off, at least its not lethal to fish.

 

[tropical-fish]

Thanks all for your input. I'm going to pick up the KH and GH test kits later today and will post up the test results.

I'll try adding a cup of CC in the filter and monitor for a few days.

 

[tropical-fish]

I was only able to get the KH test as GH was sold out.

Tested the tank water and the tap water. Both have the same result. The color goes yellow right at the first drop. So that's a 0-50ppm reading.

I picked up some crushed coral and I've added a cup full into the filter. Let's see how it goes.

 

[Rivercats]

API makes a test kit that has both the Kh and Gh tests in it. Saves you from buying 2 different test kits.

 

[tropical-fish]

Ok it's now 24 hrs since I added the crushed coral and the ph is just below 7. Normally is the ph expected to continue to rise over the next few days?

If so I'm considering removing some of the coral.

Thanks.

 

[Rivercats]

It may or may not depending on how much buffer it's adding into the tank and what ph you want. You may need to add more but wait 2-4 days.

 

[tropical-fish]

ideally i'm aiming for a ph of 6.5 to 7 so if it holds steady at this it's spot on.

i'll keep a close eye on it over the next few days.

Thanks for all your help.