[Chocoholic]

I have a moderately planted, low tech, 55 gal tank. I set it up 4 months ago. I have it stocked with 7 juvenile M. Bosemani which range from 1.5 to 2 inches long. I change 50 percent of the water once a week. Untreated well water. No ferts. Water chemistry- ammo 0 , nitrites 0 nitrates 5-10. Ph is usually about 7.8

The problem is that I have had the ph crash to 6.0 twice for no discernible reason , that I can figure out( which is why I am posting). Everything was like usual and then I noticed the fish hovering at the bottom and not swimming actively as usual. I tested the water and the ph had crashed to 6.0(possibly lower as 6.0 is the limit of my testing kit). Yikes! I did a big water change( about 80 percent) and the ph went up to 7.4, fish went back to normal. This has happened twice in the last 4 months.

What could this be from? I would like to add shrimp but I am not sure if they could tolerate this type of shift.

 

[AdamTill]

What's your KH? Substrate?

 

[Diana]

What is the KH of the well water?
Does it change over time?

 

[touch of sky]

As the previous posters have said, check your KH. Either buy a test kit, or take a sample of your water to your local pet store. Most of them will check your water for you at no charge. I would take a sample of water from your tap and one from your tank. The KH (carbonate hardness) level in your water is what holds ph steady. A reasonably high KH will hold the ph steady. If the KH is low, the ph can drop.

 

[Chocoholic]

Substrate is eco complete. I don't know what the kh is. I will bring a sample from the tap and the tank to have it tested.

 

[dukydaf]

When did you observe these pH swings ? After water change ? Dosing something ? Feeding live food ? In the morning ?

What have you done differently before the pH swing ?

 

[Chocoholic]

Actually I have a test strip. GH 150, KH 100-120 the same in the tank and from the tap. But I did an 80 percent water change yesterday.

 

[SwissCheeseHead]

I'll say that test strips are notoriously inaccurate and that you should use a liquid test kit. You'll get more accurate consistent readings with the liquid test kits. You should invest in the API Master test kit. It has testing solution for ammonia, nitrites, nitrates, pH, and high pH. They also have test kits for GH and KH as well, but that is separate from the master test kit.

Bring a sample from your tap, your tank, and also sample from when you observe the fish behaving strangely and get them tested, either from your LFS or the test kit.

 

[Hoppy]

How are you testing the pH? Test strips? What brand test kit? Etc. Unexplained sudden changes can be a problem with how you tested it.

 

[Chocoholic]

Ok, I was able to use a friends liquid drop test. The kh of tank is 80 and that of the tap slightly higher at 90. She did not have a test for GH. She has one for total calcium; I don't know if they are the same.

And I was feeding live blood worms about an hour before the last ph crash. I have never fed live foods before; I have only fed frozen and rehydrated freeze dried food. Do live foods cause decreases I the ph?

 

[Diana]

It looks like something is removing the KH from the water, if the tests are correct- Strips suggested the KH was a bit higher, now the test is showing the tap and tank are not the same, the tank is lower.
What is the pH (even if it just from the strips)?

Some substrates can remove the carbonates from the water. Some of the ADA products can do this, Safe-T-Sorb and related substrates can do this.
When the KH drops the pH is likely to drop, too, and can get quite low. It took lab quality tests to show my pH was in the low 5s when this happened in some of my tanks.

You can add carbonates by adding baking soda. It is sodium bicarbonate.
1 teaspoon of baking soda added to 30 gallons will raise the KH by 2 German degrees of hardness (about 35ppm).
Always include the units when you report test results or any other numbers.
When I added this much to my tanks the pH came up from 'below the bottom of the test' to 6.2. The KH rose from 0 degrees to 2 degrees.

Calcium is not the same as GH. Calcium is one of the materials measured as GH.

I also find the strips a bit 'off' at times, but they are useful to follow trends.

I have never noticed a pH problem with live foods.

 

[Chocoholic]

Would decomposing food and mulm remove carbonate and thus lower the ph?

 

[Diana]

Yes.

Anything decomposing is being decomposed by microorganisms. Some of these use the carbon from carbonates.

Organic matter (leaves, fish waste, fallen food, driftwood...) in general contributes to the acidity of the water.
Does the same in the garden, beneficial to alkaline soil.

When the filter is doing a good job a lot of the debris in the tank is getting trapped in the sponges and floss. This has not removed these materials from the system, they are still decomposing in the tank system, just out of sight. Best thing you can do is to keep the filter clean when it just barely starts slowing down. Do not let the debris accumulate to the point that the filter is flowing too slow.

 

[WaterLife]

How sudden is this pH crash?
You mentioned it happening twice over a 4 month period. Is the pH going from 7.8 to 6 (or less) overnight? Over a two day period? Weeks time? In a month? 7.8 gradually lowering to 6 in two months?

As Diana mentioned, organic matter and decomposition by microorganisms lead to the water turning more acidic.
But as far as I know, microorganisms produce co2. Not sure which microogranisms take carbon from carbonates.

If 7 juvi boesemani in the 55 gallon is all you have, that's not much of a fish bioload by itself to contribute to the pH lowering as quickly as it is.

How is your maintenance on the tank? Tank very dirty? Filter very dirty? How often do you clean out the filter? How often do you vacuum the substrate (mulm, detritus, etc)? How often do you do water changes and what %?

I take it you are not injecting co2, correct?
What kind of plants do you have? Any fast growers?
How many hours do you leave the light on?
Plants can resort to stripping carbon from the KH (thus lowering KH) if they have no other option.

I've heard others mention that higher CEC substrates, Eco Complete being one of those, can strip away carbonates from the water (lowering KH). I don't know too much about that. I am wondering if the KH/PH is higher near the substrate (not much, slowly leaching out into nearby lower water), explaining why the fish are hanging at the bottom since they find that area more comfortable for them. Fish in water pH not to their liking don't just stay at the bottom of the tank, they still will venture around the tank, though a lot less active, often just hovering around. Haha just a wild "what if" though. I wonder just how much KH they would strip until they are "saturated", though it should stabilize very soon by now.

Is there any driftwood in the tank that is leaching out a lot of tannins or is rotting?

By the way, if you are referring to dwarf shrimp such as Neocaridina Red Cherry Shrimp, they will probably be eaten by the rainbows, especially when the boesemani are adults, even the adult shrimp will likely be gone.

 

[Nordic]

Strong/medium low light? I'm wondering if our friend, biogenic decalcification is at work here.

As we learned, 1g of food will produce 1g of CO2 over 24 hours, which in itself would lower pH I guess this would somewhat combat decalcification, unless you have very strong lighting.