Singapore has very soft water from what I've heard, same as we have in my area. The pH from the tap may be high, but with no buffering capacity due to 0 kH that's gonna drop as soon as it hits your tank. For reference, my tap water is around pH 8 but my degassed tank water is 6.2-6.4. The good thing is low KH isn't really an issue for plants and fish, you can essentially ignore your kH and to a certain extent your pH.
Low kH does mean that it's very hard to measure your CO2 levels through the kh-pH relationship as liquid test kits have trouble measuring very low pH. Your water will have a pH around 5.2 at 30 ppm CO2, which is out of the working range of many liquid pH test solutions. The easiest way to go is with a drop checker.
Definitely get some GH booster though. The all in one fertilizers don't contain nearly enough calcium for healthy plant growth, and are probably short on magnesium as well. I don't know about K levels on APT Complete but it probably wouldn't hurt to have a little extra as well. I aim for 4 GH.
Related to stirring up dirt... If it's causing an algae bloom to disturb the surface of the substrate that means you should be doing it more often, not less. I clean the substrate with either a gravel vac or turkey baster every time I do a water change. You have to pick up all those algae spores and mulm in there or the slightest imbalance will cause an algae bloom.
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As for CO2, I have mine going on one hour before lights on. It should not take more than a few minutes to see some CO2 bubbles out of your diffuser.
Thank you both for the help!
- yeah, water in Singapore is really soft! I'll get myself a drop checker ASAP, probably the one from CO2 Art. I gather than positioning the drop checker closer to the substrate is the best position for it but I'm not really sure if there's space in there for one. I'll have to think about where to put it.
I think I'll also start stirring up the soil with a pipette and siphoning it up each water change. I don't have a turkey baster but a pipette is essentially the same thing anyways.
Having to mess with the GH every water change sounds like a major pain but I did bring it up in the first place. Shooting for 4 dGH as a start sounds like a pretty good plan. APT Complete probably doesn't have a whole lot of calcium or magnesium in it and my tap water definitely won't have enough... The most easily available product here is probably Seachem Equilibrium, but I'm not sure if it's any good. It also has potassium in it since you mentioned it. Just for reference, 1ml of APT per 2L of water is supposed to add 4ppm of K. I really have no idea what is an optimum ppm to shoot for, which is why I'm using an AIO fert in the first place but I'm wondering if there's an alternative to Equilibrium that doesn't have quite so much potassium in it. If Equilibrium is as good a product as any other than I'll probably just get that.
Also, do I add the booster directly into the tank after I'm done with my water change? I'll kind of have to do it by trial and error but since water straight out the tap has nearly 0 GH i could probably just add the appropriate amount into the tank. I reckon after taking into account all the stuff in the tank that the actual volume of water in there is 23L or so.
- I'll take a note of how long it takes the CO2 to hit the diffuser tomorrow. The last time I took note of this was quite a while back, but I recall that it took nearly 30 minutes. But then again I wasn't watching the diffuser the whole time. I think I'm using nearly 2m of tubing as well and the cylinder is actually located just below the tank so I could probably shorten the tube a fair bit.