PH problem in 8G Biocube

[FishNutzBoi]

Here's some spec's:
8G biocube
10 lbs of LR
10 lbs of LS
Maxijet900 return pump
50W Stealth heater
2nd chamber is cleared of bioballs and added w/ LR rubbles

I started cycling the tank with a piece of raw shrimp last saturday. As the shrimp started decomposing, the tank smelled pretty bad so I knew the nitrogen cycle was kicking in. But about 3 days later the smell was gone and algae was breaking out (i forgot the name but its the brown algae that always comes after the cycle). So I tested the water and:

NH3: 0
NO2: 0
NO3: 20
PH: 7.4 <---- PROBLEM!

I did a 5G water change and put 3 hermit crabs in there and they are doing well.

What caused this PH problem?

I noticed that because of the hood, the evaporation was almost unnoticeable. The water just evaporates and get caught under the hood then drips back down into the tank :eek:

TIA

[Saltwaterstart]

I would say that the tank is still in the young phase of cycling. It will take a while to stabilize in Ph. The only tip I could offer is to aerate and raise the alkalinity. It is probably pretty low right now. You could always try a buffer, but they only work for short periods of time.

[Mr. Buck]

umm i had the same problem in my 12g AP and when i told the guy at the LFS about it he put a "little bit" of buffer in a ziploc and i mixed a tsp of that in just enough fresh water and then dumped it in and it worked great my ph is just right now and it helped my alkalinity im sure if youve got a good LFS they might just give you a little bit.

[FishNutzBoi]

The return outlet is pointed a little upward to break the water surface so I don't think aeration is a problem.

I will try dosing kalkwasser using my ATO and see what happens.

I also have another theory for the problem:

I bought 10G SW from a LFS because I didn't want to mix my own SW (big mistake). The tested the water's salinity and it was only at 1.022. The guy said they were using Kent salt. Would it be possible the low PH is from the premixed water I bought?

I'm making my own SW now.

[FishNutzBoi]

Mr. Buck 1 dose of buffer has helped maintain your PH ever since?

[mathias999us]

If you cycle is over, I would suspect one of the following:

1. Bad pH test kit - they are notoriously inaccurate. What does a fresh batch of SW measure with this kit?

2. You need to measure your alkalinity. Aside from vigorous aeration to equilibrate your tank water to the CO2 level in the air in your house, your pH is a direct function of your alkalinity. If you have low alkalinity, you will definitely have low pH.

3. You have elevated CO2 in your house air or in your tank. If it's house air that's high, aerating with air from outside, like hooking your skimmer air intake to a hose that goes outside, or opening a window near the tank with this can help with this. Pretty much he only reason you would have excess CO2 in your tank would be if the cycle is actually still occuring, and you have non-photosynthetic organisms giving off large amount of CO2 through respiration, which will happen during the cycle. A partial solution to this is to increase aeration, such as with an airstone. Often times, surface agitation alone is not sufficient to equilibrate water CO2 levels with air CO2 levels in a timely manner. And, waiting for the cycle to finish...

You should read through some of Randy Holmes-Farley's articles in the chemistry forum. These are important concepts to understand.