Who Gives A Fish Forums

I'm in a bit of a bind with my tank right now. It's lightly stocked, low-tech, and heavily planted, but I've got a sizable filter that's keeping my N levels really low. Between the filter and the plants, I've got hardly any nutrients available. This has led to some... interesting learning experiences. I've been doing fewer water changes because my N levels are undetectable, but when I let the water sit, my pH and TDS creep up. My pH is already at 8.3, so I'm not thrilled about it getting any higher.

To keep things in check, I've been doing 15-20% water changes every week with RO water. But of course, this wipes out any N I've managed to build up. I've started dosing with root tabs and I'll be adding fertilizers to the water column soon – I've been hesitant because of the algae, but I think it's time. My main question is, what's causing this pH and TDS increase? I've only added RO water, which is running at 6.5 and 8.1ppm, and I've got Seachem Flourite black substrate, some bogwood, and "blue stone" rocks from a local rockyard. The only thing I can think of is that the rocks are the culprit – or maybe it's the biohome in my sump? I'm really grasping at straws here.

Has anyone else dealt with a background pH and TDS increase? If so, what was the cause? I'd love to hear your thoughts and see if there's something I'm missing.

I'm no expert on TDS, but from what I understand, it's not just about the usual suspects like ammonia, nitrite, and nitrate. Everything that's dissolved in the water contributes to the TDS reading - fish waste, tannins from the bogwood, phosphates from their food, you name it.

If you're really concerned the rocks are the culprit, here's a simple test you can try. Fill two tubs with water and test them right away to make sure they're identical. Then, pop one of the rocks into one of the tubs and test the water daily. The other tub serves as a control - any difference between the two is likely down to the rock. If the rocks are indeed causing the issue, it should become apparent in the test tub within a few days.

I've never been a fan of obsessing over TDS measurements - it's a bit of a red herring if you ask me. As sSjey mentioned, every time you add food or anything else to the tank, the TDS is going to increase. It's just a fact of life in aquarium keeping.

Nitrogen isn't the be-all and end-all of tank health, either. If you've got a planted tank, the plants will use the ammonia produced by the fish and food. But that's not the only reason we change water. I change 75% of the volume in each of my tanks every week, and I do it regardless of the nitrogen readings. In my opinion, it's just the easiest way to keep a healthy tank.

Fish live in their own waste, and there are all sorts of things floating around in that water that we can't measure - pheromones, hormones, bacteria... you name it. Changing a significant portion of the water every week is just a good way to keep all that stuff under control. And it works - all my tanks are planted, and the plants are thriving.

I've been wondering about the "blue stone" rocks I picked up from a local rockyard, and whether they might be contributing to my pH and TDS issues. I've been trying to research what exactly "blue stone" is, but I'm not finding much information. Does anyone have any knowledge about this type of rock, or experience with it in their tank?

sSjey wrote: ↑Wed Jan 26, 2022 12:50 pm I'm no expert on TDS, but from what I understand, it's not just about the usual suspects like ammonia, nitrite, and nitrate. Everything that's dissolved in the water contributes to the TDS reading - fish waste, tannins from the bogwood, phosphates from their food, you name it.

If you're really concerned the rocks are the culprit, here's a simple test you can try. Fill two tubs with water and test them right away to make sure they're identical. Then, pop one of the rocks into one of the tubs and test the water daily. The other tub serves as a control - any difference between the two is likely down to the rock. If the rocks are indeed causing the issue, it should become apparent in the test tub within a few days.

I'm still stumped by the blue stone - it looks nice, but I have no idea what it's doing to my water parameters. I just can't seem to figure out how my 6.6 RO water is ending up as 8.2 aquarium water.

That 'Blue stone' appears to be a mix of various materials, potentially including mineflakes. If it contains something like lime, it could be the culprit behind your pH and TDS issues.

I've dug up more info on the blue stone - turns out it's a type of sandstone, and it can contain lime. Does that sound plausible to you as the culprit behind my pH and TDS increase?

I'm seriously impressed you took the time to look that up - thanks for going the extra mile. It doesn't exactly scream sandstone to me, I mean it doesn't have that gritty texture. I'd be more inclined to believe it's mudstone, but honestly, who knows. The thing is, it's definitely possible it's got something in it that I don't want in my tank, maybe even heavy metals. I think I'll grab a piece and try dripping some HCL on it to see how it reacts. And yeah, I know I've been putting it off, but I should probably take @sSjey's advice and soak a few to see what happens. If I'm being honest with myself, those rocks are the only real variable in the tank that could be causing the pH to spike.

I'm genuinely curious about the outcome now, go ahead and test it.

I guess I've got no choice but to give in to the peer pressure. Testing those rocks just jumped to the top of my to-do list, and I'll be sure to share the results once I've got them.