Having trouble keeping my co2 levels up

I have a 120 gallon tank, my tap water pH is 7.8 and KH 5 so I'm going for an end of day pH of 6.7. For the last two weeks though it's been dropping less and less throughout the day until it stopped dropping at all, so I left the co2 on overnight for a few nights. The morning after the first night the pH was 6.7, exactly where I want it, and by 3 pm it was 7.6+ (I didn't bother figuring out what exactly it was, that was too high). I left it on overnight again and the next morning the pH was still 7.6+. I bumped up the bubble rate to a stream but the pH stayed there through the day and is the same this morning.


Three or four weeks ago I put a Rex Grigg style reactor on, replacing a leaky MaxMix reactor. I don't know if it's related - seems like it should be working better now, not worse - but it's worth mentioning. I also put a surface skimmer on the tank several days before this started, and I suppose that could contribute to the problem, so I turned it off this morning to see what happens.


Any ideas what the problem is or how to fix it? It seems very odd that the pH is going up through the day, when the co2 is on. And it's giving me algae.

 

I'm checking pH with an API test kit and using a drop checker to keep an eye on it as well.


I checked the reactor for leaks yesterday, and just checked again to be sure, but I didn't find any. The co2 line connector to the reactor body is a slightly translucent white and I can see a little water backed up into it and co2 bubbling through that into the reactor. Which would make me think it's just not enough co2, except that it has been in the past...

 

The reactor is plumbed inline with a Fluval 406 after the filter, then to in inline heater. I can take pics.


I cleaned the filters on sunday, they seem to be putting out good flow but I have no way to objectively measure that. I also have a Fluval 306 on the opposite end of the tank, which is where the surface skimmer is.

 

I do have seiryu stone, and aquasoil. I just tested the KH, it's 5, which is the same as my tap water which I also just tested, so I don't think they're affecting the KH. The GH in the tank is higher than my tap, 4 in tank and 0ish from the tap. Which is confusing because I do have a KCL water softener, but the salt hasn't been filled for a while and the tap GH was 8 when I've tested it over the last three weeks or so. Connection?


The pH does not usually go down more after a water change.


Interesting that I could have had the opposite effect by adding more co2 because of buildup in the reactor. That could be my problem.


In the photos you can see the reactor has a valve on it, which I think is to increase flow if you have a filter with really high gph. I've had it partway open before and I could hear water trickling inside so I figured my flow was too low to need it. I wonder if I can work some air out by opening and closing it though.

 

This morning the drop checker was green and the pH tested at around 6.7 after leaving the co2 on all night again. I submerged my bubble counter and check valve, and am sure neither leak. It now seems most likely to me that air is building up in the reactor and causing it to be less effective.

The drop checker has been staying blue-green. It was green this morning though. The pH test kit has always agreed with the drop checker also.


I do need to get another check valve, I thought I had a better one but couldn't find it, so this "temporary" one has been on it for too long.


The black box below the power strip is the control box for my Current USA light.


The heater needs to be vertical and I don't have space for that before the filter, the tubing would have to make a sharp turn back upward to the filter. The head pressure could be part of my reactor problem.


I've heard putting the heater before the filter is bad for the motor also, because of the added heat?

Do you prefer sumps then, or just particular canister filters?


I don't think I have ever gotten my pH to 6.5 0_o

 

Hmm maybe if I just crack the valve it will help...


I'm a little annoyed with the company I bought the reactor from, because I had asked them what size would be appropriate for my tank and filter before I bought it, and this was their recommendation. But I really think you would need something like an fx5 with this one.

 

I left the valve open a little, the pH went up overnight again with the co2 on. So that didn't help...

 

I don't have another diffuser. I could get a powerhead, I've just never found that to be very effective with the one I have, even in smaller tanks. Maybe I could figure out a better setup for it that what I had done before.

 

I do have seiryu stone, but the pH seems to stay pretty stable, it doesn't go up over what my tap water tests at.


I've decided to try to just start over. I purged as much air as I could out of the reactor by turning off the co2, opening the valve all the way and unplugging the filter then plugging it back in until it pushed all the air out and I no longer hear any trickling inside it. Then I started the co2 back up at 1bps and am bumping it up by about 1 bps per day until I either get the desired pH change or get a buildup of air, whichever happens first. If it seems like I can't get the reactor to work correctly I guess I'll get a diffuser.