My Fluval = Cyano but Low PH?

[Gibeon]

Well, I've had an ongoing low profile battle going with cyano for the past couple months. It stays to the back of the tank and I scrape it off during water changes. (Once a week, using Real Ocean boxed water for water changes. Gib=Lazy).

I have always cleaned the fluval at night and had noticed a little bit of something on restart. Last night I netted the output when restarting it and I collected probably an 1/8 to a 1/4 cup of uneaten food that had been sucked into the fluval and then been stuck in the return tubing (it's ribbed like an accordian and I think that may be the cause). It was incredibly disgusting - hundreds of tiny brine and mysid carcasses (carcai?).

I am now going to be turning off the canister filter during feedings and see if that helps out. I think too much of the food was getting sucked into the Fluval and left to rot.

I really, really need to get a skimmer.

The question is whether a lot of decaying fish food would be holding my PH back. OR do I have a bad PH test kit. My Alk is right at 10-11 dKH and Ca is at 420 or so. O2 is around 8 degrees. Ammo, N03, N04, all = Zero

My PH is stuck at around 7.8... and I'm not really sure how to get it higher.

[aquaman3680]

the fuvals, or any external canister filter, generally will bring down pH too.

[BoomerD]

Yep. Canisters as a rule, are not great for reef tanks. They trap a lot of detritus, become biological filters, which in turn, generate lots of nitrates. The "other" Boomer may chime in with an explanation of why they tend to push the pH down, as chemistry isn't one of my strong suits...
You'll find very few reefers who use canisters of any kind, except for the occasional carbon filtration. I used a Magnum 350 for a LONG time just for carbon filtering and polishing the water, but only for about a week per month, then I took it down and cleaned it for the next time. Most use lots of live rock as their main filter, supplemented by a GOOD protein skimmer.

[lcstorc]

I run a canister on my system, but that is in addition to lr and a skimmer. So far no problems, but who knows what is next.
What are your phosphates? When I was having a cyano issue in the seahorse tank the problem was high phosphates combined with low flow.
While it sounds like you need to do something about the canister you should check your phosphates as well during the cyano battle. I have had good luck with Phosban to reduce the phosphates as well as rinsing all food with r/o before feeding.
Not sure about the ph. That one sounds like a Boomer question.

[Gibeon]

I can't wait to see what Boomer says.

Unfortunately, I do not have a good phosphate test kit. It ALWAYS reads 0, which just can't be right.

I do have about 35 lbs of live rock, but no skimmer. I'm using carbon and purigen in the canister until I get a skimmer going, then I'll switch it out to just purigen. I like that the canister adds a gallon or two of H20 to the tank, as I don't have a fuge or sump yet either... So much to do...

Thanks for the input!

[tatuvaaj]

Gibeon,

The PO4 test kit reading of "zero" means just the kit is not sensitive enough to measure the PO4 level in water. The reasult itself is probably correct but unfortunately not very usefull One very good PO4 test kit is Salifert that can measure as low as 0.015 ppm PO4.

There are a couple of ways how canister filters can contribute to low pH. First of all, the heterotrophic bacteria living inside the filter will consume oxygen and give out carbon dioxide just like you and me. The CO2 will lower pH. The other mechanism is incomplete nitrification-denitrification cycle that will produce extra acid that will lower the pH. In well aerated (skimmer!) tanks where denitrification (live rocks and sand bed) occurs these effects should IMHO be minor.

One thing about most cyanobacteria (and most benthic algae on coral reefs) is that they do not get majority of their nutrients from water column but from the substrate they grow on. Several in-situ experiments on reefs have shown that adding nutrients to the water column don't increase the cyanobacteria growth that much. Instead lack of predation and competition can cause blooms. So in most cases of cyanobacteria blooms in aquarium I would argue that it's because of increased nutrient release from the substrate they grow on.

[lcstorc]

Interresting Tatu. Learn something all the time around here.
Thanks for the info.