Large Drop in pH - 7.8 in Tap, 6.0 in Tank

Geoff

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I first set up my tank on June 21 and ran the filter for almost a week (tank only had blasting sand and water in it). I added fish on June 27, along with TSS. On July 2, I tested the water, and my pH was 7.8. On July 4, it was still 7.8. But then the next day, July 5, it was 6.8. On July 6, it was 6.8 again. July 7 and 8 it was 6.4. And finally, both yesterday and today it was 6.0.

Now I know that we should generally just leave our pH alone and that most fish will adapt to whatever pH your water is. However, I'm concerned with the large drop. From what I understand, drops in pH are more harmful to fish, and if the water I put in is 7.8 and then it keeps dropping to 6.0, isn't that a not-so-good thing? This happened in the past as well. When I first started keeping fish 2 years ago in April 2013, my pH was 7.8 for months and months. Then suddenly it started dropping to 6.0 in my tanks (I had 4-5 tanks running). I haven't had fish for the past year and some months, so I don't know what my pH would have been last year. I know I tested the hardness way back when, and it wasn't very high.

On Monday I put in a cuttlebone in the hopes that raising my hardness will buffer the pH, but as you can see above, my pH just kept dropping. I'm also concerned about establishing/maintaining a cycle with a pH of 6.0. This evening, I tested the pH and hardness of my tank water and the pH and hardness of my tap water. Here are the results:

Tap:
ph - 7.8
GH - 3-4
KH - 4

Tank:
ph - 6.0
GH - 5-6
KH - 2

I tested the KH in both water twice and got the same results.

What do you make of this? Should I attempt to harden my water in order to maintain the 7.8 pH when I add the tap water during water changes? I would prefer not to deal with chemically altering things, but I do have the cuttlebone in there (which didn't seem to work?) and today I bought a bag of crushed coral. I could put some in a bio bag and put in one of my filter media baskets. But I wanted to lay out the situation here first.

My parameters right now are:
Temp: 79
pH: 6
Ammonia/Nitrite/Nitrate: 0

It's been that way since Sunday. Previously I had Nitrate readings of 5 on July 2 and 10 on July 4 (0 ammonia and nitrite both times) but then Sunday I noticed my barbs gasping at the surface. I tested and had 5+ nitrite. Did 2 50% water changes, and it was down to 0 by Monday morning. I've had the same results every day since then, except for the pH dropping over the course of the week. So I had thought the TSS was starting to work but then with the high nitrite spike and the large water changes, I think I killed the cycle. I've started dosing the tank with Stability per bottle instructions. On day 2 of that.

Fish in the tank are:
1 pearl gourami
7 Cherry barbs
6 sterbai corys

Tank is 36g non-planted with Black Diamond blasting sand for a substrate. I have a Fluval 406 canister filter running.
 
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Geoff

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Does anyone know why my pH would drop like that? Is it strictly because of the hardness?
 

Dom90

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Yes I think that has a big part to do with it. The loss of KH.




@CindiL could probably explain it better to you than I ever could. A low KH will cause a PH crash. You may want to use Replenish to restore your KH and use aragonite or crushed corals to buffer your pH at around 8-8.2.


 
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Geoff

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I read the stickies on pH, GH, and KH and I get it in general. Just wasn't sure if I was missing something.

I'd rather try naturally increasing my KH rather than chemically. (Is Replenish a chemical?)
 

CindiL

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Yes, your KH being at 2 will not have enough carbonates in the water to hold your ph at 7.8.
The crushed coral is a good idea and will help buffer your water in the future. It should help hold your KH.

In the meantime you can use start using some plain old baking soda to get your KH (and ph) back where it should be. You can add in 1tsp at a time (mixed in with a little tank water) and it will almost instantly start rising a small amount. Normally, when just buffering water that is still holding its ph, you can add in 1tsp per 10g and this will raise your KH by about 4 or 5 dKh. At that amount it shouldn't alter your ph much if any. Because yours has already dropped, I would do it more slowly.

The crushed coral should help the GH some as well. Replenish will only raise GH, not KH so it won't help your buffering capacity. Coral, limestone, argonite should all help with both I believe.

Also with water changes you can add in baking soda or buy Seachem's Alkaline buffer which will do the same thing and raise your KH, holding your ph steady.


 
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Geoff

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So if 1tsp per gallon won't be enough to raise my pH, how much do you think I'll need? Should I just add (slowly) and test until I see my pH rise? Like maybe 1tsp per gallon every hour or something?

How much of the crushed coral should I put in my filter? Half a cup? I think I read that somewhere, that starting with a half cup is recommended?
 

CindiL

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Yeah, just to be safe, 1 tsp per hour or every 30 minutes. I'm being conservative I admit. Normally its 1tsp per 10g to raise KH by 4 dKh (or 4 drops).

I think 1/2 cup coral is a good place to start like you are thinking. You will probably end up adding more but see if that holds it.


 
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Geoff

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1 tsp per gallon per hour/30 mins or 1 tsp per hour/30 mins? Sorry for the questions, just wanted make sure I'm understanding you right.

And thank you CindiL and Dom90 for helping me.
 

Thai Aquarium owner

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If you decide to go the Baking Soda route for a short term fix, be very careful of adding this stuff too quickly.
Only a small amount will raise the Ph along with the Kh, and you need to monitor both frequently when adding the baking Soda, as a rapid rise could possibly shock your fish
 
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Geoff

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How much and how often do you recommend? I was planning on testing before each time I added baking soda.
 

CindiL

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How much and how often do you recommend? I was planning on testing before each time I added baking soda.
I would just start out with 1tsp period. Definitely not 1 tsp per gallon ever. 1tsp per 10gallons which is what you would do if your ph was already where you need it to be. Does that make sense? Add the tsp, monitor it. It probably won't go up much. Wait an hour or so, test, see where you're at and add in another tsp.
 
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Geoff

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Yep I believe I got it now. Thanks a bunch. I'll have to head to the store in the am to get me some baking soda.
 

Dom90

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You don't have it in your kitchen for cooking? lol.

P.S. water changes would get your ph back up too tonight.
We both know Geoff dont do any cooking! Geoff, is there a way you could get some substrate that is aragonite-based and kind of mix it with your current substrate for a more permanent solution?
 
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Geoff

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Geoff, is there a way you could get some substrate that is aragonite-based and kind of mix it with your current substrate for a more permanent solution?
Yeahhhh, I don't think so haha. I mean, I could, but I don't wanna. I put a couple mesh bags of crushed coral in my filter this morning. And I started dosing with baking soda about a half ago.
 
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