Yeah mate, that's just not good enough at all. This is why the Ludwigia is melting.
From that data, you need to be at least pH 5.3 at Lights on 16:00.
I say "at least because it looks like your KH is very low so it moves easily with small changes in acidity. You'll probably need it to drop to below 5, but try 5.3 as a target value for now.
Try this: remove the grill from the filter inlet and place the diffuser directly under the open tube so that all the bubbles go into the filter. Repeat the measurements. You can start the measurements at gas ON 15:00. The Gas-ON measurement is our reference. From Gas-ON to Lights-ON you need to drop the pH by a full unit. And remember that you are only using one bulb now. Imagine how difficult things will be with two bulbs....
Cheers,
From that data, you need to be at least pH 5.3 at Lights on 16:00.
I say "at least because it looks like your KH is very low so it moves easily with small changes in acidity. You'll probably need it to drop to below 5, but try 5.3 as a target value for now.
Try this: remove the grill from the filter inlet and place the diffuser directly under the open tube so that all the bubbles go into the filter. Repeat the measurements. You can start the measurements at gas ON 15:00. The Gas-ON measurement is our reference. From Gas-ON to Lights-ON you need to drop the pH by a full unit. And remember that you are only using one bulb now. Imagine how difficult things will be with two bulbs....
Cheers,