Hello!

I have a 15 gal. planted tank that has been running for about 6-7weeks now, and I'm noticing some issues with a couple plants. For reference, the tank inhabitants are 5 African Dwarf Frogs, 3 otocinclus, 3 amano shrimp, a nerite snail, and some Malaysian trump snails (I think 2) and bladder snails.

I am using a finnex 24/7 planted+ CRV light, and I do have a glass aquarium lid (I hate it, but frogs might jump). It's at its brightest (not the MAX setting, but the brightest I have it at) for 6 hours, I'm not sure the % of each color, but I am thinking of upping the lighting, the only algae I have is some green spots on the glass.

My parameters are as follows:

Nitrite & Nitrate: 0

pH: 7.5

KH: 80

GH: 60-120

Note: last night I took a measurement and it said both my GH and KH were 0, but that's not possible??? I use tap water and switched from RO water a couple weeks ago, and have been doing weekly water changes? Idk it's weird?? Every other time it has been hard water, since the water here is VERY hard.

Ammonia: 0

I dose 2x a week with ThriveS. Note that I used to use RO water (NOT remineralized) and recently (2-3 weeks ago) switched to just dechlorinated tap water.

Note: I do a ~30% water change once a week.

The plants that are looking a little funky are my s. repens, which has some green dotting now, it used to be quite healthy and normal. Not every (s. repens) plant has this.

I also noticed that my hygrophila difformis is like ... "disintegrating"? Pieces are browning and then coming off in small bits. Some leaves look healthy but others are doing this weird melting stuff. I've had this plant since day 1 and it was always super healthy up until recently. A few bigger pieces have floated off.

Lastly, I noticed that my in ludwigia palustris, all the lower leaves fell off! It was in the back, right near the light, but I think it was shaded by an anubias and java fern, which I have moved. I'm hoping it does better now, but some leaves at the bottom are still turning yellow and coming off, and it's not very red.

Could it be the glass lid? It's new, but the hygrophila difformis has been suffering since before then...idk.

My suspicion would be that a drastic change in water parameters has either shocked the plants or caused some other water parameter to go off. Plants also need nitrates, so having that at zero is potentially problematic. What made you switch from RO to dechlorinated tap? Are your KH/GH measurements in degrees or ppm? Cause in degrees, that's some pretty hard water overall. How are you measuring that? Surely not a liquid test kit...

I've known s. repens to be rather finicky with water parameter changes. The green spots are only on the s. repens? Cause it sounds like green spot algae, but I'd expect it on the anubias first. That algae can be from too much light, especially if it's on the glass, so you may not need to up the lighting. And the ludwigia in that hard of water with no CO2 will probably never turn very red. You may get an yellow/orangey or pink color out of it, but this should be on the upper leaves, not the lower ones. You may be better off to trim the tops off the ludwigia and just replant them and remove the lower bits that are struggling. You could leave them in to see if they sprout side shoots I suppose.

What made you go with Thrive S instead of Thrive C which is formulated for low tech tanks?

Overall though I'd think about reintroducing some RO water to drop the TDS and hardness a little bit if you still have the means to do so. The plants will probably survive without it after some acclimation, but would certainly do better in softer, more acidic water. And probably need to up your dosing to get some more nitrates. Cause if the nitrates are down, probably other nutrients are low too.

Answering Your Questions/Comments:
1. I switched because my frog was having issues and some LFS told me harder water would help him. Their reasoning wasn't the best but I was desperate. He ended up passing away despite me trying very hard to save him

2. Ha that would be an oof. I'm using the API 5-in-1, so it's in ppm -- would plants only start showing signs this late after the switch? Full-on breakage even in like "hardy" plants?

3. Weirdly enough, it isn't on the anubias...? I'm wondering if the spots are actually damage instead of algae? I do have some on the glass though

4. I was worried about my amano shrimp and the copper. Do you think that is something I should be worried about? If not, and C is "better," I'll happily switch

5. You're probably right, I'm planning on increasing. In terms of RO, do you know whether getting an RO machine (is it a machine?) is practical, or should I keep buying it? And how quickly should I reintroduce softer water?

If you have an RO suggestion on what to purchase I'm all ears bro

Another Thing:

I just did a water check and something weird happened and I was wondering if you could help?

My tap water is hard like I've said, and as I said it’s been like at least two weeks since I did my first water change to replace RO water. So I’ve probably done 2-3 now with tap, each 30-50 percent.

But I just checked my water and it says my pH is suddenly 6.5 and my hardness is 0?! I’m pretty sure I measured it after adding tap the first couple times and it was hard af like my tap water?!

But now it’s soft again...? I checked my tap with the same strips and sure enough it came back super hard.

I’m so confused