end of cycle PH drop?

[ejk0799]

I have to shout from the rooftops for a second...The end is in sight!!!

Saturday will be 6 weeks with my 75 gallon freshwater and I am thrilled that my cycle is almost complete. I have a couple of questions now though...

My ammonia this morning finally tested 0 after an eternity of being way too high. :clap:

My Nitrites tested at 2.0 (maybe a little higher, color is subjective). When they too drop will it be gradual or like someone flipped a switch?

My PH is what threw me though. It was at 7.6 at it's highest and I got it down to 7.0 and then this morning after not testing it for a week, it tested at 6.4. Does this sudden, rather significant drop have something to do with the end of the cycle and the ammonia drop or is it something I should take corrective action with? My water temp is 76 and there are 4 fishy friends living in there.

Last question. I have never checked for Nitrates because I was told there aren't any until the cycle is complete. Should I go buy the test kit for it now?

Thanks!

 

[rrkss]

The cycle convert ammonia which is a base and raised the pH to Nitric Acid HNO3 which is a strong acid and lowers pH. Alkalinity also known as KH nuetralizes the pH lowering effects by accepting the protons or H+ ions. A pH of 7.6 in your starting water is pretty low so your KH probably is not that high either. I have relatively soft water myself so I like to add 1/4 teaspoon of baking soda per 10 gallons of water I change during a water change. This mitigates any affects on pH from the cycle.

 

[indiginess]

yes, the pH drop has to do with the nitrogen cycle, as rrkss alluded to. in addition to nitric acid, there may also be traces of nitrous acid (the acid nitrite forms in water).

since you have fish in the tank, i would do a waterchange. what does your source water test at for pH and KH? you are going to get the most accurate results by testing your water after it sits for a couple of hours.

when ammonia decreases, and nitrite readings start to spike, the end is definately near. in my experience, the nitrite fall is closer to a switch than a gradual fall, but they can get pretty lethal during the spike. again, i'd recommend a decent sized waterchange. 30-50%, since you have fish in there.

if i were stuck on a deserted island with only one test and an established aquarium, i would chose a nitrate test. IMHO.

in short, i would do a larger waterchange, both for pH corrective measures and nitrite reduction. you may get false-low nitrite production readings for a little while, but your fish will be at less risk for life-shortening damage.

you wont be certain the cycle is finished until you see nitrite fall to zero for a couple of days, and nitrates on the rise.

good luck

 

[ejk0799]

Thank you both. I will go do a 30% water change now and continue to wait patiently for this to be done so I can finally add some new residents.

 

[echoofformless]

Only one thing I want to add - the end of nitrites can sometimes take considerably longer than the ammonia. This is not always the case, but I have heard (and experienced) nitrites lasting up to a month.

 

[ejk0799]

If I have to wait another month for these **** Nitrites to come down, our members on the West Coast will here me scream all the way from Connecticut.