pH trying to crash at end of cycle?

[mozzer]

So I'm at Day 20 in my fishless cycle and the last 2 days I've had 0 ammonia and 0 nitrites, and around 80 nitrates. The problem is, my pH seems like it's trying to crash.

Throughout the cycle my pH has been pretty constant at 7.5, but the last 2 days it has gone to 7.0 and then 6.8 last night. I did 60-75% PWCs the last 2 nights.

This morning, I checked (12 hours since last night - I'm so anxious for this to complete so I can add fish) and the pH is 6.6, ammonia 0, nitrites 5.0 ppm, and nitrates 80 ppm. I'm really hoping the nitrites will be back down to 0 again tonight and something isn't going drastically wrong.

Is this to be expected? What should I do, if anything? Another PWC?

 

[Cloudhp8]

I have heard the PH may swing if the cycle is not yet complete. And once complete would stabilize. With Nitrites showing up it may not be done....how have you been cycling the tank? using pure ammonia or adding food to the tank?
60 - 75% PWC could be a reason to the swing.....??
Do you have any wood or rock? or added any new to the tank recently? I know that can swing PH as well....maybe not that drastically over a night or 2
Any real plants?
adding any chems? what kinds?
I would say maybe stick it out and wait a little while longer to see if it goes back to being stable before putting fish in....don't want to rush it and have fish dying

 

[mozzer]

I have plants, driftwood, and lava rock and have been dosing Florish Comp and Excel. All this has been the same since day one. I'm hoping the nitrites are there only because I last tested the water only 12 hours ago. I've been ammonia and nitrite free for 3 days dosing 4.0 ppm each night.

I'm not sure what else I can do since I did PWCs the last 2 nights to prevent what seems to be a crash.

 

[jlk]

This is very common towards the end of a fishless cycle. Your bb are in full swing and are processing a large amount of ammonia in a very short period of time. They need carbonates/buffers (KH) to do this. As the buffers are utilized processing the ammonia, your ph becomes unstable. The more they use, the more unstable your ph becomes and the further it will crash. Kind of a vicious cycle. The drop in ph and lack of buffers will also affect how well your bb are processing your ammonia- they can be quite sensitive.

Lets see how how things look at the 24hr mark. I would suggest a big wc (75%+) then only dose 2ppm of ammonia and lets see how things look in 24hrs. If your ph continues to be an issue, you may need to add a bit of buffer to your filter to help stabilize things (crushed coral or aragonite).

 

[mozzer]

So, the 4 ppm of ammonia is quite high and serves well to get the cycle going, but once it gets going 4 ppm becomes too much, correct?

I will do the large PWC ASAP. If my tank can cycle the 2 ppm and read 0 ammonia and 0 nitrite in 24 hours, is the cycle complete?

 

[jlk]

4ppm is kind of the standard for a fishless cycle. Some forums recommend more, some recommend less. Your tank sounds cycled already based on a few days of steady zeroes from 4ppm. Lets see how it does with 2ppm just make sure your bb were not adversely affected by the ph drops. If all is well, I would say your complete!

 

[mozzer]

I'm just getting to the water change now. After testing, pH is 6.8 (a little higher than this morning), ammonia and nitrites are 0, and nitrates are 80.

 

[armymp327]

ammonia is also alkaline and high amounts will cause the PH to rise, so your PH was high because of the 4PPM ammonia, and when all of that ammonia was used up your PH went back down to normal.

 

[mozzer]

12 hour check in: pH 6.8, ammonia and nitrites 0 ppm, and nitrates 40 ppm. It seems my buffers were used since pH was 7.5 after the water change (and before adding ammonia). I suppose this fluctuation would occur every time I do a PWC. Does this mean I need to add the buffers? If so, do I add them to my canister filter and how much?

 

[jlk]

Have you done a test on your tap water yet? We need to rule this out first before considering a buffer unless you want to keep your tank at 7.5. Place some tap water in a container with an airstone or bubbler. If you dont have an extra, just give the water a good stir every so often to help release dissolved gasses. Test the ph in 24hrs and lets see if it drops. I suspect it may.

If you simply want to keep your tank at 7.5, then adding a small amount of buffer in a mesh bag/piece of clean pantyhose to your filter housing will help. It may take a bit of experimentation to figure out a good amount that will keep your ph stable but not create a big jump. Please ask if you have questions!

 

[mozzer]

I'll try the tap water test after 24 hours. I also suspect the pH will drop. Just out of the tap, the pH is 8.4.

I use a Python for PWCs with tap water. My question then is should I be keeping the pH at 7.5 so there isn't a discrepancy when I do a PWC? Will a discrepancy be bad for the fish?

I'd rather not mess with the pH, but it seems like I need to do something.

 

[jlk]

Quite a few people have a big difference between what their ph is straight from the tap vs what it reads after dissolved gasses have left the water. Unless there is a huge difference between your initial tap ph and what the actual tap reads after sometime (ie, it drops from 8.4 down to 6.5), I would not be overly concerned. Lets see how the ph looks in 24hrs.

 

[mozzer]

The pH of my tap water after standing 24 hours is 7.5, but what does that tell me? Thanks so much for your help!

 

[jlk]

Thats fine! Atleast there was not a huge drop and it just indicates your bb are using up your KH to process ammonia creating the ph drop your seeing right now. If you want to get technical, you could have the KH tested at a decent lfs (tap & tank) to see if it may be on the low side. Generally though, the ammonia output of normally stocked tank is nowhere near the amount of ammonia you have been adding so there should not be any problems once you have fish as long as you do decent weekly wcs. If you do start to see some drops when you have fish, a small amount of buffer should help keep things stable.

 

[mozzer]

Fantastic!! This is exciting news! I may pick up an API kit for hardness just for informational purposes, and I'll definitely keep a close eye on the pH. Thanks again for lending a hand to someone just getting started!