Figuring Out My Hc Cuba


New Member
Oct 5, 2019

I have been fighting my HC Cuba / DHG tank for some time and I just cannot seem to figure out what part of the puzzle I am missing.

Here is some background information:

50 Gallon Tank
CO2 is injected via a reactor and water is output via a Lilly Pipe. (Starts two hours before first light and stops one hour before light goes off). Overall flow is around 5-6x an hour.
PH: 8.2 (water left out over night), around 7.1 when photo period starts and 6.4 by the end of the day. Measured using an Apera PH20, which I have calibrated.
HG: 7
KH: 7
Temp: 23C / 73F
Light: Chihiros RGB 901 Series A Plus (30 minute ramp and then 5 hours at 65%)
Fert: NILOCG Thrive 4.3ml every day
Excel: 5ml every other day
Water: RO remineralized with GH/KH to 120 TDS. I only remineralize every other 50% water change as the rocks I have in the scape appear to be bumping up GH/KH quite a bit (Seiryu Stone, or whatever passes for it these days). I do 2x water changes a week.
Ammonia: .25ppm
Nitrate: 20 - 40ppm depending on the water change
Substrate: Tropicana Soil Power top layer with Ecocomplete as a bottom layer.

Overall, both the HC and and DHG do not seem to be reacting very well. The Cuba is growing new leaves, but they turn brown with algae after a few days, and many times will dislodge and float off. I originally suspected diatoms, but my tank is now 4 months old, and I am pretty well filtered with decent flow, there is only one big rock in my tank and water goes around it, which I can see on the plants. DHG is doing the same good new growth but browns after a while. I am not getting very many long HC Cuba strands, however the strands I do get stay close to the substrate but again, everything browns. The HC Cuba does not look "spindly" like a CO2 problem pictures I have seen but that continues to be my go to since that is what everyone recommends. See the attached photo.

Stocking is 20 Cherry Barbs, 15 Neon Tetras, 4 otos and about 15 Amanos

The fish do not seem to have any issue with the CO2 at my current level, but my Amano shrimp at the end of the day start dancing quite a bit and usually a few will dart toward the surface, fall upside down, turn blue and just twitch for a few hours like they have been poisoned. They almost always survive and this only appears to happen to the larger Amanos. 6.4PH is on the outside of their comfort range based on my understanding.

Since the fish are tolerating the CO2 I want to increase it some more, but I am worried about the shrimp and the PH just seems like it is swinging way too much. I tried to do the one PH drop method and I didn't see good results at the 7.0 level of PH. 6.4 PH seems to be where I have gotten good new growth, it just doesn't last. I have a PH drop checker at the bottom of the tank and it is very very yellow. I have moved to a few spots to confirm I do not have any dead spots in my flow.

So overall, just looking for some advice. I tried switching to an in tank diffuser for the CO2, but that resulted in a pretty bad melt, and so while my flow was good it may not have been good enough push the bubbles around in time before they float to the top. I also tried increasing the photo period to six hours at 75% and that just resulted in more brown algae (no green algae)

Thanks for any help on this one. I am running out of ideas to try.


photo 2.jpg